Bump korthout/backport-action from 2 to 3 (#2455)

Bumps [korthout/backport-action](https://github.com/korthout/backport-action) from 2 to 3.
- [Release notes](https://github.com/korthout/backport-action/releases)
- [Commits](https://github.com/korthout/backport-action/compare/v2...v3)

---
updated-dependencies:
- dependency-name: korthout/backport-action
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/merge.yml

@@ -30,7 +30,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - name: Create backport pull requests
-        uses: korthout/backport-action@v2
+        uses: korthout/backport-action@v3
 
   # Upload nightly docs to the website
   docs: