Variable is persisted in activty after deleting it from workflow context

## Steps to Reproduce
see workflow


1 create workflow ^ with 2 variables (ie var1 and var2) (see attachment)


2) set 'set variable' activity output to one of those activities (var1 or var2)
3) save publish and run the workflow - see that it works

4) delete the variable from the workflow context, see that in the 'set variable' output/ the variable is no longer selected.


5) save and publish+ run the workflow
6) expect an error when running workflow because 'set variable' no longer has a var( undefined)
8) see that activity still sets value to the deleted variable


3. **Attachments**:

[act-branching-3-join.txt](https://github.com/user-attachments/files/20753794/act-branching-3-join.txt)

4. **Reproduction Rate**: Indicate how often the bug occurs when following these steps (e.g., "every time", "intermittently: about 50% of the time"). Always.

## Expected Behavior
Throw error

## Actual Behavior
values are being written to vars that are no longer existing

## Environment
Elsa 3.5 and 3.2.