packages/registry/rubygems: Fix typo of "you Gemfile" => "your Gemfile"

[issyl0]

Why:

There was a typo on https://docs.github.com/en/packages/working-with-a-github-packages-registry/working-with-the-rubygems-registry#installing-a-package.

What's being changed:

There was a typo on https://docs.github.com/en/packages/working-with-a-github-packages-registry/working-with-the-rubygems-registry#installing-a-package.

Check off the following:

• I have reviewed my changes in staging. (look for the deploy-to-heroku link in your pull request, then click View deployment)
• For content changes, I have reviewed the localization checklist
• For content changes, I have reviewed the Content style guide for GitHub Docs.

Writer impact (This section is for GitHub staff members only):

• This pull request impacts the contribution experience
  • I have added the 'writer impact' label
  • I have added a description and/or a video demo of the changes below (eg. a "before and after video")

[welcome]

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[lee-dohm]

Looks good to me

[github-actions]

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