perf: speed up action downloads (#1209)

An action pinned to a full commit hash cloned the whole repository, and a cached one hit the network on every run. Now only the pinned commit is fetched at depth 1, a cached commit is reused with no network at all, and the action's `.git` directory no longer ships into the job container, matching GitHub.

```
repo                  cold ms         warm ms       cache KiB
actions/checkout      5807 → 787    1064 → 12    11492 → 2349
actions/setup-node   15257 → 1013   1365 → 21    64303 → 9924
actions/cache        18782 → 760    1589 → 16    60890 → 12507
actions/setup-go      5513 → 764     589 → 20    16600 → 9104
docker/login-action  25809 → 1225   1288 → 10    81709 → 12503
```

Reviewed-on: https://gitea.com/gitea/runner/pulls/1209
Reviewed-by: bircni <bircni@icloud.com>
Co-authored-by: silverwind <me@silverwind.io>

act/filecollector/file_collector.go

@@ -94,10 +94,11 @@ func (cc *CopyCollector) WriteFile(fpath string, fi fs.FileInfo, linkName string
 }
 
 type FileCollector struct {
-	Ignorer   gitignore.Matcher
-	SrcPath   string
-	SrcPrefix string
-	Handler   Handler
+	Ignorer    gitignore.Matcher
+	SrcPath    string
+	SrcPrefix  string
+	SkipGitDir bool
+	Handler    Handler
 }
 
 func openGitIndex(path string) (*index.Index, error) {
@@ -124,6 +125,12 @@ func (fc *FileCollector) CollectFiles(ctx context.Context, submodulePath []strin
 		if fi.IsDir() && len(split) > 0 && split[len(split)-1] == "." {
 			return nil
 		}
+		if fc.SkipGitDir && split[len(split)-1] == ".git" {
+			if fi.IsDir() {
+				return filepath.SkipDir
+			}
+			return nil
+		}
 		var entry *index.Entry
 		if i != nil {
 			entry, err = i.Entry(strings.Join(split[len(submodulePath):], "/"))