ci: bump korthout/backport-action from 3 to 4 in the actions group

Bumps the actions group with 1 update: [korthout/backport-action](https://github.com/korthout/backport-action).


Updates `korthout/backport-action` from 3 to 4
- [Release notes](https://github.com/korthout/backport-action/releases)
- [Commits](https://github.com/korthout/backport-action/compare/v3...v4)

---
updated-dependencies:
- dependency-name: korthout/backport-action
  dependency-version: '4'
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: actions
...

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

.github/workflows/backport.yml

@@ -24,7 +24,7 @@ jobs:
           private-key: ${{ secrets.BACKPORT_KEY }}
 
       - name: Create backport PR
-        uses: korthout/backport-action@v3
+        uses: korthout/backport-action@v4
         with:
           pull_title: "${pull_title}"
           label_pattern: "^ci:backport ([^ ]+)$"