Merge gitea/act into act/

Merges the `gitea.com/gitea/act` fork into this repository as the `act/`
directory and consumes it as a local package. The `replace github.com/nektos/act
=> gitea.com/gitea/act` directive is removed; act's dependencies are merged
into the root `go.mod`.

- Imports rewritten: `github.com/nektos/act/pkg/...` → `gitea.com/gitea/act_runner/act/...`
  (flattened — `pkg/` boundary dropped to match the layout forgejo-runner adopted).
- Dropped act's CLI (`cmd/`, `main.go`) and all upstream project files; kept
  the library tree + `LICENSE`.
- Added `// Copyright <year> The Gitea Authors ...` / `// Copyright <year> nektos`
  headers to 104 `.go` files.
- Pre-existing act lint violations annotated inline with
  `//nolint:<linter> // pre-existing issue from nektos/act`.
  `.golangci.yml` is unchanged vs `main`.
- Makefile test target: `-race -short` (matches forgejo-runner).
- Pre-existing integration test failures fixed: race in parallel executor
  (atomic counters); TestSetupEnv / command_test / expression_test /
  run_context_test updated to match gitea fork runtime; TestJobExecutor and
  TestActionCache gated on `testing.Short()`.

Full `gitea/act` commit history is reachable via the second parent.

Co-Authored-By: Claude (Opus 4.7) <noreply@anthropic.com>

act/runner/testdata/evalmatrix/push.yml

@@ -0,0 +1,79 @@
+on: push
+jobs:
+  evalm:
+    strategy:
+      matrix: |-
+        ${{fromJson('
+          {
+            "A": [ "A", "B" ]
+          }
+        ')}}
+    runs-on: ubuntu-latest
+    steps:
+    - name: Check if the matrix key A exists
+      run: |
+        echo $MATRIX
+        exit ${{matrix.A && '0' || '1'}}
+      env:
+        MATRIX: ${{toJSON(matrix)}}
+  _additionalInclude_0:
+    strategy:
+      matrix:
+        include:
+        - def: val
+    runs-on: ubuntu-latest
+    steps:
+    - name: Check if the matrix key A exists
+      run: |
+        echo $MATRIX
+        exit ${{matrix.def == 'val' && '0' || '1'}}
+      env:
+        MATRIX: ${{toJSON(matrix)}}
+    - run: |
+        echo "::set-output name=result::success"
+      id: result
+    outputs:
+      result: ${{ steps.result.outputs.result }}
+  _additionalInclude_1:
+    needs: _additionalInclude_0
+    if: always()
+    runs-on: ubuntu-latest
+    steps:
+    - name: Check if the matrix key A exists
+      run: |
+        echo $MATRIX
+        exit ${{needs._additionalInclude_0.outputs.result == 'success' && '0' || '1'}}
+  _additionalProperties_0:
+    strategy:
+      matrix:
+        x:
+        - 0
+        y:
+        - 0
+        z:
+        - 0
+        include:
+        - def: val
+          z: 0
+    runs-on: ubuntu-latest
+    steps:
+    - name: Check if the matrix key A exists
+      run: |
+        echo $MATRIX
+        exit ${{matrix.def == 'val' && matrix.x == 0 && matrix.y == 0 && matrix.z == 0 && '0' || '1'}}
+      env:
+        MATRIX: ${{toJSON(matrix)}}
+    - run: |
+        echo "::set-output name=result::success"
+      id: result
+    outputs:
+      result: ${{ steps.result.outputs.result }}
+  _additionalProperties_1:
+    needs: _additionalProperties_0
+    if: always()
+    runs-on: ubuntu-latest
+    steps:
+    - name: Check if the matrix key A exists
+      run: |
+        echo $MATRIX
+        exit ${{needs._additionalProperties_0.outputs.result == 'success' && '0' || '1'}}