Fix sending event messages to non-subscribers

[lwatt]

Closes https://github.com/dask/distributed/issues/7013

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

[GPUtester]

Can one of the admins verify this patch?

Admins can comment ok to test to allow this one PR to run or add to allowlist to allow all future PRs from the same author to run.

[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  ±    0         15 suites  ±0   6h 13m 7s :stopwatch: + 14m 16s   3 151 tests +  60    3 058 :heavy_check_mark: +  57    85 :zzz:  -   3    8 :x: +  6  23 315 runs  +501  22 379 :heavy_check_mark: +498  913 :zzz:  - 18  23 :x: +21 

For more details on these failures, see this check.

Results for commit 43a9cbdf. ± Comparison against base commit 3655f136.

:recycle: This comment has been updated with latest results.

[lwatt]

Thanks - I've added a test now. Confirmed this fails on the original version, and passes now.

[lwatt]

I've just pushed the linting updates from pre-commit. It would be great if this could be merged soon

[hiiwave]

@lwatt I was bothered by this today. Thanks for the fix! I see this PR was approved. Could we merge it now?