fixes wrong ::set-output name

[Chrico]

Why:

The documentation uses run: echo "::set-output name=random-id::$(echo $RANDOM)" but the outputs says random-number and the text below as well.

What's being changed:

changes run: echo "::set-output name=random-id::$(echo $RANDOM)" to use random-number

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[github-actions]

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Source	Preview	Production	What Changed
content/actions/creating-actions/creating-a-composite-action.md	Modified	Original

[github-actions]

Thanks for opening a pull request! We've triaged this issue for technical review by a subject matter expert 👀

[github-actions]

This is a gentle bump for the docs team that this PR is waiting for technical review.

[ethomson]

LGTM, thanks!

[ramyaparimi]

@Chrico
Thanks so much for opening a PR with this fix! I'll get this merged once tests are passing 🍏

[github-actions]

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