Document limitation with reusable workflows

[unchris]

Why:

Closes https://github.com/github/docs/issues/22746

If you create a reusable workflow in repository A and that workflow uses a composite action defined also in repository A, you cannot use the reusable workflow from repository B.

This community discussion does a good job illustrating the issue, but basically the upstream workflow assumes that the composite action will be in the context of repository B's files when it should be looking in repository A's files.

What's being changed (if available, include any code snippets, screenshots, or gifs):

I'm adding a limitation to the Limitations section for Reusable Workflows.

Check off the following:

• [x] I have reviewed my changes in staging (look for the "Automatically generated comment" and click the links in the "Preview" column to view your latest changes).
• [x] For content changes, I have completed the self-review checklist.

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[github-actions[bot]]

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This comment is automatically generated and will be overwritten every time changes are committed to this branch.

The table contains an overview of files in the content directory that have been changed in this pull request. It's provided to make it easy to review your changes on the staging site. Please note that changes to the data directory will not show up in this table.

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Content directory changes

You may find it useful to copy this table into the pull request summary. There you can edit it to share links to important articles or changes and to give a high-level overview of how the changes in your pull request support the overall goals of the pull request.

Source	Preview	Production	What Changed
actions/using-workflows/reusing-workflows.md	fpt ghec ghes@ 3.7 3.6 3.5 3.4 ghae	fpt ghec ghes@ 3.7 3.6 3.5 3.4 ghae

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fpt: Free, Pro, Team ghec: GitHub Enterprise Cloud ghes: GitHub Enterprise Server ghae: GitHub AE

[cmwilson21]

@unchris Thank you for opening a PR and linking it to your issue! ✨

We appreciate all the info. I'll get this triaged for review! ⚡

[github-actions[bot]]

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