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>

modules/actions/jobparser/model.go

@@ -269,7 +269,7 @@ func EvaluateConcurrency(rc *model.RawConcurrency, jobID string, job *Job, gitCt
 	}
 
 	matrix := make(map[string]any)
-	matrixes, err := actJob.GetMatrixes()
+	matrixes, err := matrixesOf(actJob)
 	if err != nil {
 		return "", false, err
 	}
@@ -510,7 +510,7 @@ func EvaluateJobIfExpression(jobID string, job *Job, gitCtx map[string]any, resu
 	// GetMatrixes always returns at least one element (an empty map for a job without a matrix),
 	// so only a non-empty combination should populate `matrix.*`, leaving it nil otherwise.
 	var matrix map[string]any
-	matrixes, err := actJob.GetMatrixes()
+	matrixes, err := matrixesOf(actJob)
 	if err != nil {
 		return false, err
 	}