Update delete_backport_branch workflow to include release-chores branches (opensearch-project#18981)

Signed-off-by: Riley Jerger <rjerger@amazon.com>

Author: RileyJergerAmazon

.github/workflows/delete_backport_branch.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     permissions:
       contents: write
-    if: github.repository == 'opensearch-project/OpenSearch' && startsWith(github.event.pull_request.head.ref,'backport/')
+    if: github.repository == 'opensearch-project/OpenSearch' && (startsWith(github.event.pull_request.head.ref,'backport/') || startsWith(github.event.pull_request.head.ref,'release-chores/'))
     steps:
     - name: Delete merged branch
       uses: actions/github-script@v7