CI: Bump ruby_docker to 4.18

What does this MR do?

CI: Bump ruby_docker to 4.18

Bump ruby_docker image to the latest image, which includes ruby 3. The addresses QA jobs failing with:

ERROR: Error installing gitlab-qa: The last version of gitlab-qa (>= 0) to support your Ruby & RubyGems was 11.3.0. Try installing it with gem install gitlab-qa -v 11.3.0 gitlab-qa requires Ruby version >= 3.0.0. The current ruby version is 2.7.4.191.

Example job: https://gitlab.com/gitlab-org/cloud-native/gitlab-operator/-/jobs/4564975696

Equivalent change in Charts: gitlab-org/charts/gitlab!3262 (merged)

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion.

Required

• Merge Request Title and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com
• When ready for review, MR is labeled "~workflow::ready for review" per the Distribution MR workflow

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added
• Integration tests added to GitLab QA
• Equivalent MR/issue for omnibus-gitlab opened
• Validate potential values for new configuration settings. Formats such as integer 10, duration 10s, URI scheme://user:passwd@host:port may require quotation or other special handling when rendered in a template and written to a configuration file.