Missing bundle install in testing pages locally

[marie-bnl]

Why:

Without doing bundle install it gives

> bundle exec jekyll serve .
bundler: command not found: jekyll
Install missing gem executables with `bundle install`

What's being changed:

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.

[welcome]

Thanks for opening this pull request! A GitHub docs team member should be by to give feedback soon. In the meantime, please check out the contributing guidelines.

[janiceilene]

@victorbnl Thanks so much for opening a PR! I'll get this triaged for review 🌟

[shati-patel]

Thank you for your contribution, @victorbnl, much appreciated! I'll get this merged shortly 😃

[github-actions]

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