Fix documentation about mapping container port to a random free host port

[mindtraveller]

Why:

I found a mistake in the docs about port mapping in the services section of the Actions documentation. This PR corrects it.

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

The documentation page is changed.

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.

[welcome[bot]]

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.

[github-actions[bot]]

Automatically generated comment ℹ️

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-containerized-services/about-service-containers.md	fpt ghec ghes@ 3.5 3.4 3.3 3.2 ghae	fpt ghec ghes@ 3.5 3.4 3.3 3.2 ghae

[cmwilson21]

@mindtraveller Thanks so much for opening a PR! I'll get this triaged for review :zap:

[github-actions[bot]]

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

[github-actions[bot]]

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

[github-actions[bot]]

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

[github-actions[bot]]

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