build(deps): bump korthout/backport-action from 3 to 4

Bumps [korthout/backport-action](https://github.com/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
...

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

.github/workflows/backport.yml

@@ -23,7 +23,7 @@ jobs:
           token: ${{ steps.app-token.outputs.token }}
 
       - name: Backport Action
-        uses: korthout/backport-action@v3
+        uses: korthout/backport-action@v4
         with:
           # Regex pattern for labels that should trigger a backport AND extracts the target branch
           # from the name (e.g. v0.x or v0.x.y; we use zerover). This action will ONLY proceed if