Upgrade backport workflow to v2 (#1884)

(cherry picked from commit 5d37ca6)

Author: JoshMock

.github/workflows/backport.yml

@@ -11,6 +11,6 @@ jobs:
     name: Backport
     steps:
       - name: Backport
-        uses: tibdex/backport@v1
+        uses: tibdex/backport@v2
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}