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 <[email protected]>
Co-authored-by: silverwind <[email protected]>

act/container/docker_run_test.go

@@ -471,7 +471,7 @@ func TestRejectsMissingContainer(t *testing.T) {
 		assert.Contains(t, err.Error(), `container "job-1" does not exist`, op)
 	}
 	check("copyContent", cr.copyContent("/var/run/act", &FileEntry{Name: "x", Mode: 0o644})(ctx))
-	check("copyDir", cr.copyDir("/var/run/act", "/src", false)(ctx))
+	check("copyDir", cr.copyDir("/var/run/act", "/src", false, false)(ctx))
 	check("exec", cr.exec([]string{"echo"}, nil, "", "")(ctx))
 	_, err := cr.GetContainerArchive(ctx, "/var/run/act/x")
 	check("GetContainerArchive", err)