avoid redundant cleanup fixture in gen_test tests

[graingert]

related to #6049

• Closes #xxxx
• Tests added / passed
• Passes pre-commit run --all-files

gen_test calls with clean() and so makes the cleanup fixture redundant

[mrocklin]

+1. Will merge on passed tests

[mrocklin]

I'm seeing the following test failure:

E               pytest.PytestUnraisableExceptionWarning: Exception ignored in: <coroutine object _needs_document_lock.<locals>._needs_document_lock_wrapper at 0x00000236567A3B40>
E               
E               Traceback (most recent call last):
E                 File "C:\Miniconda3\envs\dask-distributed\lib\warnings.py", line 506, in _warn_unawaited_coroutine
E                   warn(msg, category=RuntimeWarning, stacklevel=2, source=coro)
E               RuntimeWarning: coroutine '_needs_document_lock.<locals>._needs_document_lock_wrapper' was never awaited

I'm guessing that this is the new warnings system being noisy, and Bokeh (or our handling of Bokeh) not being clean.

[graingert]

Yep, see also bokeh/bokeh#11976

The allowlist of unawaited Coroutines are here: https://github.com/dask/distributed/blob/main/setup.cfg#L62

[mrocklin]

Woot. Thanks for fixing upstream

[github-actions]

Unit Test Results

       16 files  +       4         16 suites  +4   7h 23m 16s ⏱️ + 1h 57m 46s
  2 737 tests +       3    2 655 ✔️ +     12       81 💤  -     9  0 ❌ ±0  1 🔥 ±0 
21 782 runs  +5 421  20 704 ✔️ +5 145  1 077 💤 +276  0 ❌ ±0  1 🔥 ±0 

For more details on these errors, see this check.

Results for commit 717ca4e. ± Comparison against base commit 7d55039.