Bump Ruby & gem versions

Closes #18 (closed)

I needed this for working on a customer's internal ticket and noticed that issue. Leaving this here, just in case it turns out to be helpful for the template generally 🤞

Essentially, this is the result of:

# updating Ruby to 3.0.2 manually
bundle && bundle update
# yarn upgrade && npm update --force # removed from the MR after all, because of build failure, see https://gitlab.com/gitlab-org/project-templates/rails/-/jobs/1430260695#L466

cc @gitlab-org/manage/import/backend