Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request? (put an "X" next to an item)

[ ] Documentation update
[ ] Bug fix (template)
[ ] New rule (template)
[ ] Changes an existing rule (template)
[ ] Add autofixing to a rule
[ ] Add a CLI option
[ ] Add something to the core
[x] Other, please explain: Fix GitHub Actions test flakiness

What changes did you make? (Give an overview)

For the last several weeks, our CI jobs have been flaky due to test hook timeouts on the Windows and macOS runners. I traced most of the failures to four before hooks that copy the test fixtures to a temporary directory. They usually take ~2.5s, but that occasionally spikes to tens of seconds: in the two times I was able to repro the timeouts, the slowest copy jobs were 25 (output) and 32 seconds.

Is there anything you'd like reviewers to focus on?

• Rather than increasing the global test timeout, I instead bumped it just for these four hooks that were causing problems. Is the narrower approach acceptable?
• The previous timeout was 10 seconds. Is 60 seconds for these four hooks too much? In 8 samples (2 successful repros × 4 hooks), the longest I saw was 32 seconds.
• Since these hooks just call out to the shell, I didn't try to do any optimization that might speed up these operations. Is there something easy I missed? My guess is that resource contention on shared runners is causing slow filesystem performance, but I haven't proven that's the original cause.