Drop Python 3.8 support

[graingert]

Closes dask/community#315

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

[github-actions]

Unit Test Results

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

       20 files   -          6         20 suites   - 6   12h 18m 58s ⏱️ - 3h 3m 36s
  3 623 tests +         1    3 516 ✔️ +         4     105 💤 ±    0  2 ❌  - 3 
35 037 runs   - 10 769  33 318 ✔️  - 10 314  1 717 💤  - 451  2 ❌  - 4 

For more details on these failures, see this check.

Results for commit dc76082. ± Comparison against base commit 6f70648.

♻️ This comment has been updated with latest results.

[hendrikmakait]

Thanks, @graingert! I just have a small question and two nits that don't block approval. From what I understand, we have lazy consensus in dask/community#315, so this should be good to merge.

[jrbourbeau]

Thanks for handling all this @graingert. Overall this looks great -- just left a few small comments / questions

Also, it looks like we can drop some compatibility code here too

distributed/distributed/deploy/cluster.py

Lines 164 to 168 in e887fde

	except asyncio.CancelledError:
	# Task is being closed. When we drop Python < 3.8 we can drop
	# this check (since CancelledError is not a subclass of
	# Exception then).
	break

[hendrikmakait]

We should change https://github.com/graingert/distributed/blob/18e5421c31b6d8ceadcfa6cfecf1228072c67606/docs/source/develop.rst#L23 as well (conda env create --file continuous_integration/environment-3.8.yaml -> conda env create --file continuous_integration/environment-3.9.yaml)

[jrbourbeau]

Thanks @graingert. This looks good to go

EDIT: Waiting for CI to finish

[jrbourbeau]

Actually, distributed/comm/tests/test_tcp.py::test_getaddrinfo_invalid_af, which is being added here, is failing in CI
https://github.com/dask/distributed/actions/runs/5069958811/jobs/9104314707?pr=7840
https://github.com/dask/distributed/actions/runs/5069958811/jobs/9104313352?pr=7840

[graingert]

@jrbourbeau just pushed a fix - I skip it on windows

[jrbourbeau]

Thanks! Though we got a failure on macOS too https://github.com/dask/distributed/actions/runs/5069958811/jobs/9104314707?pr=7840

[graingert]

@jrbourbeau weird, I pushed a skip for that too

[jrbourbeau]

The gpuCI failures here look unrelated to this PR but I've not seen them before (cc @charlesbluca). Checking over in #7857.

Will merge this PR and dask/dask#10295 after we've confirmed they're not related

[jrbourbeau]

Okay, seeing similar gpuCI failures over in #7857, so they're definitely unrelated to the changes here

[jrbourbeau]

Thanks @graingert @crusaderky @hendrikmakait