fix(ci): derive the image name from GITHUB_REPOSITORY

[argoyle]

The Github CI provider derived the image name from the last path element of RUNNER_WORKSPACE:

CIBuildName string `env:"RUNNER_WORKSPACE"`

func (c *Github) BuildName() string {
	if c.CIBuildName != "" {
		return c.Common.BuildName(filepath.Base(c.CIBuildName))
	}
	...
}

That holds on GitHub Actions, which checks out to /home/runner/work/<repository>. It does not hold on Gitea Actions, which checks out to /workspace/<owner>/<repository> and exports the parent of the workspace, so the last element is the owner:

platform	RUNNER_WORKSPACE	filepath.Base
GitHub Actions	/home/runner/work/myrepo	myrepo ✅
Gitea Actions	/workspace/myorg	myorg ❌

Images were published as <registry>/<owner>/<owner> instead of <registry>/<owner>/<repository> — for us, oci.example.com/myorg/myorg — and every deployment referencing the expected name failed to pull with a 404.

This stayed hidden for as long as the Gitea runner left RUNNER_WORKSPACE unset, because the empty value fell through to Common.BuildName("") → filepath.Base(cwd), and the working directory basename is the repository name. Once the runner started exporting the variable, the name changed under us with no change on our side.

GITHUB_REPOSITORY is <owner>/<repository> on both platforms and names the repository directly, so this prefers it and keeps the previous paths as fallbacks. On GitHub Actions the result is identical to before.

Tests

Two new cases in pkg/ci/github_test.go: one for a GitHub-shaped workspace (asserting no behaviour change) and one for the Gitea layout, where RUNNER_WORKSPACE points at the owner and GITHUB_REPOSITORY has to win. Reverting the fix turns the Gitea case red and leaves the GitHub one green. TestGithub_Override_ImageName still passes, so an explicit IMAGE_NAME continues to beat both.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.90%. Comparing base (52a6510) to head (b879366).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1708   +/-   ##
=======================================
  Coverage   90.89%   90.90%           
=======================================
  Files          40       40           
  Lines        1923     1924    +1     
=======================================
+ Hits         1748     1749    +1     
  Misses        113      113           
  Partials       62       62           

Flag	Coverage Δ
unittests	90.90% <100.00%> (+<0.01%)	⬆️

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