Debug worker client

[hayesgb]

When a worker_client is created within an async function with separate_thread=True, the secede()call fails, since the running thread is also the main thread. This PR validates that the worker_clientis not running in the main thread before calling secede().

• Closes Cannot call worker_client() from an asynchronous function #5513
• Tests added / passed
• Passes pre-commit run --all-files

[GPUtester]

Can one of the admins verify this patch?

[github-actions]

Unit Test Results

       18 files  ±  0         18 suites  ±0   9h 41m 52s ⏱️ + 19m 28s
  2 702 tests +  5    2 617 ✔️ +  3       82 💤 +1  3 ❌ +1 
24 166 runs  +45  22 943 ✔️ +41  1 219 💤 +3  4 ❌ +1 

For more details on these failures, see this check.

Results for commit 49fe650. ± Comparison against base commit ccb0362.