Specify allowed contexts in jobs.<job_id>.services.<service_id>.image

[piotrekkr]

Why:

Documentation does not mention if and which context variable can be used in jobs.<job_id>.services.<service_id>.image. From my tests a subset of contexts can be used and those are: github, matrix, strategy, needs, vars and inputs.

Unfortunately, using env context is not possible. Not sure why that is. Anyhow, specifying allowed contexts in docs would be helpful when writing workflows.

I've also changed conditional service creation example because it contained invalid example that was using options context which does not exist.

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

Added a note about allowed contexts and fixed example conditional service creation.

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[github-actions[bot]]

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Source	Preview	Production	What Changed
actions/using-workflows/workflow-syntax-for-github-actions.md	fpt ghec ghes@ 3.13 3.12 3.11 3.10 3.9	fpt ghec ghes@ 3.13 3.12 3.11 3.10 3.9

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

[nguyenalex836]

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

[hubwriter]

@piotrekkr - Thanks for raising this PR. I've asked the development team to confirm your changes before we go ahead and merge this.

[piotrekkr]

Closing this pull request because there is a list of available contexts in each configuration sections here.