gh-action: bump dependabot/fetch-metadata from 2 to 3

Bumps [dependabot/fetch-metadata](https://github.com/dependabot/fetch-metadata) from 2 to 3.
- [Release notes](https://github.com/dependabot/fetch-metadata/releases)
- [Commits](https://github.com/dependabot/fetch-metadata/compare/v2...v3)

---
updated-dependencies:
- dependency-name: dependabot/fetch-metadata
  dependency-version: '3'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/dependabot-automerge.yml

@@ -14,7 +14,7 @@ jobs:
     steps:
       - name: Dependabot metadata
         id: metadata
-        uses: dependabot/fetch-metadata@v2
+        uses: dependabot/fetch-metadata@v3
         with:
           github-token: "${{ secrets.GITHUB_TOKEN }}"
       - name: Enable auto-merge for Dependabot PRs