Bump google/mirror-branch-action from 1.0 to 2.0

Bumps [google/mirror-branch-action](https://github.com/google/mirror-branch-action) from 1.0 to 2.0.
- [Release notes](https://github.com/google/mirror-branch-action/releases)
- [Commits](google/mirror-branch-action@c6b07e4...30c52ee)

---
updated-dependencies:
- dependency-name: google/mirror-branch-action
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

.github/workflows/mirror.yml

@@ -21,7 +21,7 @@ jobs:
     steps:
       - name: Mirror action step
         id: mirror
-        uses: google/mirror-branch-action@c6b07e441a7ffc5ae15860c1d0a8107a3a151db8
+        uses: google/mirror-branch-action@30c52ee21f5d3bd7fb28b95501c11aae7f17eebb
         with:
           github-token: ${{ secrets.FLUTTERMIRRORINGBOT_TOKEN }}
           source: 'main'