Dependabot with GitHub Enterprise should support updating actions from the enterprise instance

[leifwalsh]

Is there an existing issue for this?

• I have searched the existing issues

Feature description

See #6829 (comment)

On an instance of GitHub Enterprise with some actions on it (both actions we've published and those from the actions org), we would like to enable Dependabot updates with the github-actions package-ecosystem. However, when we do, dependabot tries to contact github.com rather than our enterprise instance in order to determine which actions can be updated. This is wrong because:

• Our instance may not have versions that match those on github.com, if we haven't synced them lately
• github.com does not contain the actions we've only published internally

Dependabot should be able to update actions by only looking at the repos in an enterprise instance.

[jeffwidman]

Did you try #6015 (comment) ?

[leifwalsh]

Oh, I didn't find that earlier. I can try it!