(Meta) CI has flaky tests

[akx]

Version: master (027b452)

Platform: GitHub Actions

Description:

Tests on master (and derived PRs) occasionally fail with cluster-related issues.

See e.g. https://github.com/redis/redis-py/actions/runs/3096445352/jobs/5012008536

This might be alleviated by #2395 (which reinstates docker healthchecks which were never functional in the first place (added in 63ebe69, 0d26117 etc.), but the health checks themselves don't work.