feat: use github app token (#31)

Signed-off-by: Patrik Cyvoct <patrik@ptrk.io>

Author: Sh4d1

.github/workflows/backport.yml

@@ -10,7 +10,13 @@ jobs:
     runs-on: ubuntu-18.04
     name: Backport
     steps:
+      - name: Generate token
+        id: generate_token
+        uses: tibdex/github-app-token@v1
+        with:
+          app_id: ${{ secrets.APP_ID }}
+          private_key: ${{ secrets.PRIVATE_KEY }}
       - name: Backport
         uses: tibdex/backport@v1
         with:
-          github_token: ${{ secrets.GITHUB_TOKEN }}
+          github_token: ${{ steps.generate_token.outputs.token }}