Use korthout Backport action (#251)

It seems to be currently maintained

Author: linawolf

.github/workflows/backport.yml

@@ -6,60 +6,17 @@ on:
 
 jobs:
   backport:
-    if: >
-      github.event.action == 'labeled' &&
-      github.event.pull_request.merged == true &&
-      startsWith(github.event.label.name, 'backport ')
+    if: github.event.pull_request.merged == true
     runs-on: ubuntu-latest
 
     permissions:
       contents: write
       pull-requests: write
 
     steps:
-      - name: Determine target branch
-        id: vars
-        run: |
-          label="${{ github.event.label.name }}"
-          target="${label#backport }"
-          echo "target=$target" >> "$GITHUB_OUTPUT"
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v 6.0.2
 
-      - name: Checkout repo
-        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v 6.0.2
+      - name: Backport
+        uses: korthout/backport-action@4aaf0e03a94ff0a619c9a511b61aeb42adea5b02 # v4.2.0
         with:
-          fetch-depth: 0
-
-      - name: Configure git
-        run: |
-          git config user.name "github-actions"
-          git config user.email "github-actions@github.com"
-
-      - name: Cherry pick merge commit
-        env:
-          TARGET: ${{ steps.vars.outputs.target }}
-          PR: ${{ github.event.pull_request.number }}
-        run: |
-          MERGE_SHA=${{ github.event.pull_request.merge_commit_sha }}
-
-          BRANCH="backport/pr-${PR}-to-${TARGET}"
-
-          git fetch origin $TARGET
-          git checkout -b $BRANCH origin/$TARGET
-
-          git cherry-pick -x $MERGE_SHA
-
-          git push origin $BRANCH
-
-      - name: Create PR
-        env:
-          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-          TARGET: ${{ steps.vars.outputs.target }}
-          PR: ${{ github.event.pull_request.number }}
-        run: |
-          BRANCH="backport/pr-${PR}-to-${TARGET}"
-
-          gh pr create \
-            --base $TARGET \
-            --head $BRANCH \
-            --title "Backport PR #$PR to $TARGET" \
-            --body "Automated backport of #$PR to \`$TARGET\`."
+          github_token: ${{ secrets.GITHUB_TOKEN }}