Process variables are deleted when concurrent execution appears

## Unit Test 
### Configuration
```java
package camunda.shared.configuration;import java.io.IOException;
import java.util.List;
import javax.sql.DataSource;
import org.camunda.bpm.engine.ProcessEngineConfiguration;
import org.camunda.bpm.engine.impl.cfg.CompositeProcessEnginePlugin;
import org.camunda.bpm.engine.impl.cfg.ProcessEngineConfigurationImpl;
import org.camunda.bpm.engine.impl.cfg.ProcessEnginePlugin;
import org.camunda.bpm.engine.impl.cfg.SpringBeanFactoryProxyMap;
import org.camunda.bpm.engine.impl.el.ExpressionManager;
import org.camunda.bpm.engine.spring.SpringProcessEngineConfiguration;
import org.camunda.bpm.extension.process_test_coverage.spring.SpringProcessWithCoverageEngineConfiguration;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.transaction.PlatformTransactionManager;@Configuration
public class UnitTestsProcessEngineConfiguration {
  @Bean
  public ProcessEngineConfigurationImpl processEngineConfiguration(
      final List<ProcessEnginePlugin> processEnginePlugins,
      final ExpressionManager expressionManager,
      final PlatformTransactionManager transactionManager,
      final DataSource dataSource,
      final ApplicationContext applicationContext
  ) throws IOException {
    SpringProcessEngineConfiguration config =
        new SpringProcessWithCoverageEngineConfiguration();
    config.setExpressionManager(expressionManager);
    config.setTransactionManager(transactionManager);
    config.setDataSource(dataSource);
    config.setDatabaseSchemaUpdate("true");
    config.setHistory(ProcessEngineConfiguration.HISTORY_FULL);
    config.setJobExecutorActivate(false); // <---
    config.setProcessEnginePlugins(
        processEnginePlugins
    );    config.getProcessEnginePlugins().add(
        new CompositeProcessEnginePlugin(processEnginePlugins)
    );
    config.setBeans(new SpringBeanFactoryProxyMap(applicationContext));
    return config;  }
}```

Here is sample process and test for it:
![[DAV-2_POC_1.bpmn]]

```kotlin
    @Test
    @DeployProcess(["DAV-2_POC_1.bpmn"])
    fun `POC 1 - variables are deleted`() {
        val builder: ProcessInstantiationBuilder = this.processEngine.runtimeService
                .createProcessInstanceByKey("DAV-2_POC_1")
        builder.setVariable("featureIssueId", 178825)
        builder.setVariable("implementationCategory", "category-value")
        builder.startBeforeActivity("Implement_feature")
        val processInstance: ProcessInstance = builder.execute();        
// waiting for task to be resolved        
BpmnAwareTests.assertThat(processInstance).isWaitingAt("Implement_feature")        
val processExecution: Execution = this.processEngine.runtimeService
                .createExecutionQuery()
                .processInstanceId(processInstance.id)
                .active()
                .list()
                .firstOrNull()!!       
// process variables are there
        assertEquals(178825, getVariable(processExecution.id, "featureIssueId"))
        assertEquals("category-value", getVariable(processExecution.id, "implementationCategory"))
        assertNull(getVariable(processExecution.id, "implementationIssue"))        
// triggering script task that will set `issueId`
        this.processEngine
.runtimeService.createProcessInstanceModification(processInstance.id)
                .startBeforeActivity("Set_issue_id")
                .execute()        
// `implementationIssue` is set by event `Implement_feature_issue_id_set` after `issueId` was set
        assertEquals(777, getVariable(processExecution.id, "implementationIssue"))        
// !!! process variables are not there after event is executed !!!
        assertEquals(178825, getVariable(processExecution.id, "featureIssueId")) // assert fails
        assertEquals("category-value", getVariable(processExecution.id, "implementationCategory")) // assert fails
    }    fun getVariable(executionId: String, variableName: String): Any? {
        return this.processEngine.runtimeService.getVariable(executionId, variableName)
    }
```

Output (last asserts): 
```
Expected :178825
Actual   :null

```
## Integration Test
### Configuration
```java
package camunda.shared.configuration;import java.io.IOException;
import java.util.List;
import javax.sql.DataSource;
import org.camunda.bpm.engine.ProcessEngineConfiguration;
import org.camunda.bpm.engine.impl.cfg.CompositeProcessEnginePlugin;
import org.camunda.bpm.engine.impl.cfg.ProcessEngineConfigurationImpl;
import org.camunda.bpm.engine.impl.cfg.ProcessEnginePlugin;
import org.camunda.bpm.engine.impl.cfg.SpringBeanFactoryProxyMap;
import org.camunda.bpm.engine.impl.el.ExpressionManager;
import org.camunda.bpm.engine.spring.SpringProcessEngineConfiguration;
import org.camunda.bpm.extension.process_test_coverage.spring.SpringProcessWithCoverageEngineConfiguration;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.transaction.PlatformTransactionManager;@Configuration
public class IntegrationTestsProcessEngineConfiguration {
  @Bean
  public ProcessEngineConfigurationImpl processEngineConfiguration(
      final List<ProcessEnginePlugin> processEnginePlugins,
      final ExpressionManager expressionManager,
      final PlatformTransactionManager transactionManager,
      final DataSource dataSource,
      final ApplicationContext applicationContext
  ) throws IOException {
    SpringProcessEngineConfiguration config =
        new SpringProcessWithCoverageEngineConfiguration();
    config.setExpressionManager(expressionManager);
    config.setTransactionManager(transactionManager);
    config.setDataSource(dataSource);
    config.setDatabaseSchemaUpdate("true");
    config.setHistory(ProcessEngineConfiguration.HISTORY_FULL);
    config.setJobExecutorActivate(true); // <---
    config.getProcessEnginePlugins().add(
        new CompositeProcessEnginePlugin(processEnginePlugins)
    );
    config.setBeans(new SpringBeanFactoryProxyMap(applicationContext));
    return config;  }
}```Test is the same as above.
Output is the same, variables are removed.

### The place variables are removed
ExecutionEntity.java
```java
...
  protected void moveVariableTo(VariableInstanceEntity variable, ExecutionEntity other) {
    if (other.variableStore.containsKey(variable.getName())) {
      // this is executed when ExecutionEntity.replace(PvmExecutionImpl execution) where commant says: // on compaction, move all variables
      CoreVariableInstance existingInstance = other.variableStore.getVariable(variable.getName());
      existingInstance.setValue(variable.getTypedValue(false));
      invokeVariableLifecycleListenersUpdate(existingInstance, this);
      invokeVariableLifecycleListenersDelete( // <-- here VariableInstanceEntityPersistenceListener.delete()
          variable,
          this,
          Collections.singletonList(getVariablePersistenceListener()));
    }
    else {
      // this is executed when new concurrent execution is created 
      // scenario 2 in PvmExecutionImpl.createConcurrentExecution()
      other.variableStore.addVariable(variable);
    }
  }
...
```

It seems like it is happening when there are `concurrent execution` takes place.