Drop unnecessary bundler install in CI
What does this MR do and why?
This slightly speeds up the CI tasks since we no longer have to download another version of bundler.
Starting with Bundler v2.3, Bundler automatically installs the
version needed in Gemfile.lock
if it's not installed already:
https://bundler.io/blog/2022/01/23/bundler-v2-3.html.
We've already crossed the Bundler v2.3 mark: Ruby 3.1.4 ships with Bundler v2.3.27, and Ruby 3.2.4 ships with Bundler v2.4.19.
Relates to gitlab-build-images!819 (merged)
Edited by Stan Hu