build(deps): bump korthout/backport-action from 1.2.0 to 2.1.0

Bumps [korthout/backport-action](https://github.com/korthout/backport-action) from 1.2.0 to 2.1.0.
- [Release notes](https://github.com/korthout/backport-action/releases)
- [Commits](korthout/backport-action@v1.2.0...v2.1.0)

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

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

.github/workflows/backport.yml

@@ -24,7 +24,7 @@ jobs:
         with:
           ref: ${{ github.event.pull_request.head.sha }}
       - name: Create backport PRs
-        uses: korthout/backport-action@v1.2.0
+        uses: korthout/backport-action@v2.1.0
         with:
           # Config README: https://github.com/korthout/backport-action#backport-action
           copy_labels_pattern: 'severity:\ssecurity'