Update Gitpod image to fix launch
EDIT: I planned to remove custom Gitpod image (!2203 (merged)), because default Gitpod image already uses latest Ruby. But it uses Ruby 3.1, and docs still depend on Ruby 2.7.6. So this MR just updates Gitpod image and syncs RVM code with official snippet https://www.gitpod.io/docs/introduction/languages/ruby It also deduplicates arguments for Docker lint.
Fixes #1232 (closed).
Edited by Anatoli Babenia