Fix main builds: appease the linter

[smudge]

/domain @samandmoore @effron /no-platform

There are a couple linter rules complaining. This will ensure that anyone who branches off of main won't have to fix them independently.

This also fixes the Ruby 3.0 build so that it doesn't inadvertently run with Ruby 3.1 in CI.

[nanda-prbot]

Needs somebody from @samandmoore and @effron to claim domain review

Use the shovel operator to claim, e.g.:

@myname << domain && platform

_{HOW TO: Claim a Review}

[jmileham]

<< domain lgtm