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/common/executor_max_parallel_test.go

@@ -0,0 +1,89 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package common
+
+import (
+	"context"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+// Simple fast test that verifies max-parallel: 2 limits concurrency
+func TestMaxParallel2Quick(t *testing.T) {
+	ctx := context.Background()
+
+	var currentRunning atomic.Int32
+	var maxSimultaneous atomic.Int32
+
+	executors := make([]Executor, 4)
+	for i := range 4 {
+		executors[i] = func(ctx context.Context) error {
+			current := currentRunning.Add(1)
+
+			// Update max if needed
+			for {
+				maxValue := maxSimultaneous.Load()
+				if current <= maxValue || maxSimultaneous.CompareAndSwap(maxValue, current) {
+					break
+				}
+			}
+
+			time.Sleep(10 * time.Millisecond)
+			currentRunning.Add(-1)
+			return nil
+		}
+	}
+
+	err := NewParallelExecutor(2, executors...)(ctx)
+
+	assert.NoError(t, err) //nolint:testifylint // pre-existing issue from nektos/act
+	assert.LessOrEqual(t, maxSimultaneous.Load(), int32(2),
+		"Should not exceed max-parallel: 2")
+}
+
+// Test that verifies max-parallel: 1 enforces sequential execution
+func TestMaxParallel1Sequential(t *testing.T) {
+	ctx := context.Background()
+
+	var currentRunning atomic.Int32
+	var maxSimultaneous atomic.Int32
+	var executionOrder []int
+	var orderMutex sync.Mutex
+
+	executors := make([]Executor, 5)
+	for i := range 5 {
+		taskID := i
+		executors[i] = func(ctx context.Context) error {
+			current := currentRunning.Add(1)
+
+			// Track execution order
+			orderMutex.Lock()
+			executionOrder = append(executionOrder, taskID)
+			orderMutex.Unlock()
+
+			// Update max if needed
+			for {
+				maxValue := maxSimultaneous.Load()
+				if current <= maxValue || maxSimultaneous.CompareAndSwap(maxValue, current) {
+					break
+				}
+			}
+
+			time.Sleep(20 * time.Millisecond)
+			currentRunning.Add(-1)
+			return nil
+		}
+	}
+
+	err := NewParallelExecutor(1, executors...)(ctx)
+
+	assert.NoError(t, err) //nolint:testifylint // pre-existing issue from nektos/act
+	assert.Equal(t, int32(1), maxSimultaneous.Load(),
+		"max-parallel: 1 should only run 1 task at a time")
+	assert.Len(t, executionOrder, 5, "All 5 tasks should have executed")
+}