Create test-ubuntu-git Docker Container for Proxy Tests

[jww3]

The test-proxy CI check has been failing since December 19, 2023.

test-proxy depends on Docker Hub container image alpine/git:latest.

  test-proxy:
    runs-on: ubuntu-latest
    container:
      image: alpine/git:latest
      options: --dns 127.0.0.1
    services:
      squid-proxy:
        image: ubuntu/squid:latest
        ports:
          - 3128:3128

It seems a recent update to alpine/git caused this test to start failing.

This PR seeks to establish a new git-enabled Linux container image hosted in the GitHub Container Image registry (ghcr.io). A subsequent PR will update test-proxy to utilize this new image.

By establishing a container image that is defined, maintained, published, and versioned via the actions/checkout repo, we insulate actions/checkout CI from external factors that introduce breaking changes.

[jww3]

I'm not convinced this block is necessary at this point. I'd like to see what happens without it first.

[fhammerl]

Is ${{ github.actor }} always the actions org?

[jww3]

I think it's whomever triggers the workflow, (I can devise a quick test to confirm), but I believe it'll still work as desired. All the examples use ${{ github.actor }}.

The explanation is a bit murky, but some documentation is here

[jww3]

github.repository_owner is another option, but I wanted to try it this way first and see if it works OK.

I figure it should help make auth-related failures in the workflow more clear. (e.g. joe triggered the workflow, but joe doesn't have the requisite permissions).

It might also be handy to see who published the image in GHCR.io in the event we need to do some forensics.

[jww3]

I see other workflows in the actions org that also use github.actor when pushing to ghcr.io including actions/runner.

[fhammerl]

LGTM