Add instruction for ignoring the Gemfile.lock file to prevent unsatisfiable dependencies warning

[revolter]

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Code of Conduct

• [X] I have read and agree to the GitHub Docs project's Code of Conduct

What article on docs.github.com is affected?

https://docs.github.com/en/pages/setting-up-a-github-pages-site-with-jekyll/creating-a-github-pages-site-with-jekyll

What part(s) of the article would you like to see updated?

https://docs.github.com/en/pages/setting-up-a-github-pages-site-with-jekyll/creating-a-github-pages-site-with-jekyll#creating-your-site

The existing instructions implicitly make you commit and push the Gemfile.lock file, which causes the default action to throw this warning:

The github-pages gem can't satisfy your Gemfile's dependencies

Additional information

Introduced by https://github.com/actions/jekyll-build-pages/pull/90.

[nguyenalex836]

@revolter Thank you for opening an issue and linking it to your PR! ✨