feat: Add support for dynamic matrix evaluation in Gitea Actions workflows (#36564)

Adds dynamic matrix evaluation to Gitea Actions: a job's
`strategy.matrix` can be built from the outputs of the jobs it needs.

```yaml
jobs:
  generate:
    runs-on: ubuntu-latest
    outputs:
      matrix: ${{ steps.set.outputs.result }}
    steps:
      - id: set
        run: echo "result=[1,2,3]" >> $GITHUB_OUTPUT

  build:
    needs: [generate]
    runs-on: ubuntu-latest
    strategy:
      matrix:
        version: ${{ fromJson(needs.generate.outputs.matrix) }}
    steps:
      - run: echo "building ${{ matrix.version }}"
```

Such a matrix cannot be expanded at planning time, so the job is planned
as a single placeholder and expanded by the job emitter once its needs
finish. Each combination is then gated by `if:` and concurrency as
usual.

- A matrix that resolves to no combination fails the job, as on GitHub.
- Expansion is capped at `MaxJobNumPerRun`.
- Workflows without a needs-dependent matrix are unaffected.

Fixes https://github.com/go-gitea/gitea/issues/25179

---------

Signed-off-by: Pascal Zimmermann <pascal.zimmermann@theiotstudio.com>
Signed-off-by: ZPascal <pascal.zimmermann@theiotstudio.com>
Co-authored-by: Claude <claude-sonnet-4-5@anthropic.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Claude (Opus 4.8) <noreply@anthropic.com>
Co-authored-by: bircni <bircni@icloud.com>
Co-authored-by: Zettat123 <zettat123@gmail.com>

services/actions/commit_status.go

@@ -54,6 +54,13 @@ func CreateCommitStatusForRunJobs(ctx context.Context, run *actions_model.Action
 	}
 
 	for _, job := range jobs {
+		// A deferred-matrix placeholder's name changes when it expands, so a status created while it
+		// waits would be orphaned. The emitter reloads the jobs after expanding and creates them
+		// then. A placeholder that reached a final status (skipped by its `if:`, cancelled with the
+		// run, or failed to expand) never expands, so it keeps its own name and still deserves a status.
+		if job.IsMatrixDeferred && !job.Status.IsDone() {
+			continue
+		}
 		if err = createCommitStatus(ctx, run.Repo, event, commitID, scopedPrefix, run, job); err != nil {
 			log.Error("Failed to create commit status for job %d: %v", job.ID, err)
 		}