Update gem ownership per handbook

Per https://about.gitlab.com/handbook/developer-onboarding/#ruby-gems:

When building and publishing Gems for GitLab make sure multiple developers have access to said Gem on RubyGems.org. This ensures a Gem doesn't end up being orphaned because the original author left, lost their credentials, passed away, etc.

https://about.gitlab.com/handbook/engineering/#publishing-a-project

Use a shared account when publishing. For example, when publishing a ruby gem to rubygems.org, use an @gitlab.com email alias when creating the rubygems.org account and place the credentials in a 1Password vault for your team.

We can use the following, similar to what is in a few other gems https://gitlab.com/search?group_id=9970&scope=blobs&search=gitlab_rubygems%40gitlab.com

  spec.authors       = ['GitLab']
  spec.email         = ['gitlab_rubygems@gitlab.com']