Invert logic for unlock_key (#782)

### Description

Please explain the changes you made here.

### Checklist

- [ ] Created tests which fail without the change (if possible)
- [ ] All tests passing
- [ ] Extended the documentation, if necessary

Author: Rotheem

app/utils/initialization.py

@@ -338,7 +338,7 @@ async def use_lock_for_workers(
 
     elif unlock_key:
         # As an `unlock_key` is provided, we will wait until an other worker has finished executing `job_function`
-        while redis_client.get(unlock_key) is not None:
+        while redis_client.get(unlock_key) is None:
             logger.debug(f"Waiting for {job_function.__name__} to finish")
             await asyncio.sleep(1)