`jobs.<job_name>.snapshot` allows `github` context but it is not listed in 'Available context' document

[rhysd]

Code of Conduct

• I have read and agree to the GitHub Docs project's Code of Conduct

What article on docs.github.com is affected?

https://docs.github.com/en/actions/reference/workflows-and-actions/contexts

What part(s) of the article would you like to see updated?

The custom images document says that the following workflow is valid. Notice that jobs.<job_name>.snapshot.if accesses github context.

jobs: 
  build:
    runs-on: my-image-generation-runner
    snapshot: 
        if: ${{ ! startsWith(github.ref, 'refs/tags/') }}
        image-name: my-custom-image
        version: 2.*
    steps:

However the context availability table does not list the snapshot (or snapshot.if) key. Not listed in the table means no context is available. So I believe the key is missing in the table and we need an update.

Additional information

No response

[Sharra-writes]

@rhysd Thanks for opening an issue! I have a bunch of things I'm trying to work through with the Actions team, but I will add this to the queue and let you know when I have an answer for you!

[github-actions]

A stale label has been added to this issue, because it has been open for 30 days with no activity. If you think this issue should remain open, please add a new comment.

[rhysd]

It's stale because of no update from maintainers 😅

[rhysd]

I added a PR for this after reading the runner implementation.