Avoid multiple WorkerState sphinx error

[jrbourbeau]

Currently our docs build is failing with

/home/docs/checkouts/readthedocs.org/user_builds/distributed/envs/8638/lib/python3.11/site-packages/distributed/diagnostics/plugin.py:docstring of 
distributed.diagnostics.plugin.SchedulerPlugin.valid_workers_downscaling:: WARNING: more than
one target found for cross-reference 'WorkerState': distributed.scheduler.WorkerState, distributed.worker_state_machine.WorkerState

This PR avoid that error by using the same workaround as

distributed/distributed/active_memory_manager.py

Lines 19 to 23 in d5edb4e

	# Needed to avoid Sphinx WARNING: more than one target found for cross-reference
	# 'TaskState' and 'WorkerState'"
	# https://github.com/agronholm/sphinx-autodoc-typehints#dealing-with-circular-imports
	from distributed import client
	from distributed import scheduler as scheduler_module

[github-actions]

Unit Test Results

See test report for an extended history of previous test failures. This is useful for diagnosing flaky tests.

    29 files  ±0      29 suites  ±0   10h 58m 20s ⏱️ - 1m 49s
 4 051 tests ±0   3 947 ✅  - 2     97 💤 ±0  7 ❌ +2 
55 799 runs  ±0  53 631 ✅  - 2  2 159 💤  - 1  9 ❌ +3 

For more details on these failures, see this check.

Results for commit 037176e. ± Comparison against base commit d5edb4e.

[jrbourbeau]

I'm going to merge this one in to get our docs build passing again. Happy to address any comments in a follow-up PR.