Mergeback v3.29.8 refs/heads/releases/v3 into main

This commit inlines runInit(), so that it is easier to repeat the
runDatabaseInitCluster() call when needed.

…oolcache

 Cleanup extract to toolcache feature flag

Also run the `rust` checks on "milestone" CLI releases, to ensure we
remain backward compatible with those versions. This was prompted by
#2960 (review)

Running this on current `main` and then on that PR should improve our
confidence we remain backward compatible.

It also turns out a probable `ruamel.yaml` update was changing a lot of
generated workflows, so I've:
* fixed the `ruamel.yaml` version to the latest in `sync.sh`
* added `yaml.width = 120` in `sync.py` to minimize (but not entirely
  remove) the number of changes
* checked in the workflows whose formatting was changed by the new
  `ruamel.yaml` version

Add risk assessment to PR template