Update CI depending Ruby 3.0 from the rc

[kachick]

Description

Using rc version is applied in #1364, but already released 3.0 without rc

It might fix Segmentation fault as https://github.com/lsegal/yard/runs/1940341250 ? 🤔
=> I think No... docker container run --user=root --volume="$(pwd)/:/usr/src/" --workdir='/usr/src/' -it 'ruby:3.0' '/bin/bash' reproduce it once.

Completed Tasks

• I have read the Contributing Guide.
• The pull request is complete (implemented / written).
• Git commits have been cleaned up (squash WIP / revert commits).
• I wrote tests and ran bundle exec rake locally (if code is attached to PR).

[coveralls]

Coverage remained the same at 93.423% when pulling fe06e86 on kachick:update-ci-ruby3 into 3590066 on lsegal:main.

[lsegal]

Thanks for your PR!

[kachick]

Thank you! 3️⃣