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

@ramyaparimi Thanks for your comment.

Let me explain this PR.
Below are links to testing Javascript Action and Docker Action.
There are Private Action and Public Action in these, and the user can choose either one.
However, the Composite Action documentation does not have this description, and users may misunderstand that they cannot choose Private Action.
In fact, I also read the docs and thought that Composite Action couldn't create a Private Action.
However, in reality, any Action can be tested in the same way. Therefore, the appearance of the document should be the same.

https://docs.github.com/en/actions/creating-actions/creating-a-docker-container-action#testing-out-your-action-in-a-workflow
https://docs.github.com/en/actions/creating-actions/creating-a-javascript-action#testing-out-your-action-in-a-workflow

I'm not a native English speaker, so corrections are welcome.

👋 Thanks so much for this PR @KeisukeShima! There was a lot of work recently done on the composite actions docs. Let us know if the information you're looking for isn't in the new docs!

We appreciate your interest and passion in improving the GitHub docs 💖