issue a ResourceWarning for unclosed RPC objects

[graingert]

• relates to https://github.com/dask/distributed/issues/6848

• [ ] Passes pre-commit run --all-files

• [ ] Tests added / passed

[github-actions[bot]]

Unit Test Results

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

       15 files  +       3         15 suites  +3   6h 46m 2s :stopwatch: + 2h 12m 37s   2 990 tests ±       0    2 901 :heavy_check_mark: +     11       88 :zzz:  -   12  1 :x: +1  22 173 runs  +4 191  21 128 :heavy_check_mark: +4 065  1 044 :zzz: +125  1 :x: +1 

For more details on these failures, see this check.

Results for commit cbc60162. ± Comparison against base commit 602148fd.