Persist workflow variables during background execution. (#6195)

Added a call to save workflow variables in the BackgroundActivityInvoker to ensure that any changes are persisted during background activity execution. This helps maintain consistency and state integrity across workflow invocations.

src/modules/Elsa.Workflows.Runtime/Services/BackgroundActivityInvoker.cs

@@ -41,6 +41,7 @@ public async Task ExecuteAsync(ScheduledBackgroundActivity scheduledBackgroundAc
         activityExecutionContext.SetIsBackgroundExecution();
         await activityInvoker.InvokeAsync(activityExecutionContext);
         await ResumeWorkflowAsync(activityExecutionContext, scheduledBackgroundActivity);
+        await variablePersistenceManager.SaveVariablesAsync(workflowExecutionContext);
     }
 
     private async Task ResumeWorkflowAsync(ActivityExecutionContext activityExecutionContext, ScheduledBackgroundActivity scheduledBackgroundActivity)