Update css_parser gem from 1.14.0 to 1.22.0

What does this MR do and why?

Bumps the css_parser gem from v1.14.0 to v1.22.0 as requested in https://gitlab.com/gitlab-org/gitlab/-/work_items/606700.

Adds a direct Gemfile constraint (>= 1.22.0) to enforce the minimum version. The gem is a transitive dependency of gitlab-lookbook, prawn-svg, and premailer, all of which support css_parser >= 1.22.0.

References

• https://gitlab.com/gitlab-org/gitlab/-/work_items/606700

Screenshots or screen recordings

N/A — no UI changes.

How to set up and validate locally

1. Run bundle exec gem list css_parser and confirm version is 1.22.0.
2. Run the test suite for mailer-related specs: bundle exec rspec spec/mailers/.

MR acceptance checklist

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