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/GITHUB_ENV-use-in-env-ctx/push.yml

@@ -0,0 +1,27 @@
+on: push
+jobs:
+  _:
+    runs-on: ubuntu-latest
+    env:
+      MYGLOBALENV3: myglobalval3
+    steps:
+    - run: |
+        echo MYGLOBALENV1=myglobalval1 > $GITHUB_ENV
+        echo "::set-env name=MYGLOBALENV2::myglobalval2"
+    - uses: nektos/act-test-actions/script@main
+      with:
+        main: |
+          env
+          [[ "$MYGLOBALENV1" = "${{ env.MYGLOBALENV1 }}" ]]
+          [[ "$MYGLOBALENV1" = "${{ env.MYGLOBALENV1ALIAS }}" ]]
+          [[ "$MYGLOBALENV1" = "$MYGLOBALENV1ALIAS" ]]
+          [[ "$MYGLOBALENV2" = "${{ env.MYGLOBALENV2 }}" ]]
+          [[ "$MYGLOBALENV2" = "${{ env.MYGLOBALENV2ALIAS }}" ]]
+          [[ "$MYGLOBALENV2" = "$MYGLOBALENV2ALIAS" ]]
+          [[ "$MYGLOBALENV3" = "${{ env.MYGLOBALENV3 }}" ]]
+          [[ "$MYGLOBALENV3" = "${{ env.MYGLOBALENV3ALIAS }}" ]]
+          [[ "$MYGLOBALENV3" = "$MYGLOBALENV3ALIAS" ]]
+      env:
+        MYGLOBALENV1ALIAS: ${{ env.MYGLOBALENV1 }}
+        MYGLOBALENV2ALIAS: ${{ env.MYGLOBALENV2 }}
+        MYGLOBALENV3ALIAS: ${{ env.MYGLOBALENV3 }}