change: enable automatically enabling automatic merging on backport PRs

Signed-off-by: Octol1ttle <l1ttleofficial@outlook.com>

.github/workflows/backport.yml

@@ -27,6 +27,7 @@ jobs:
         uses: korthout/backport-action@v4.4
         with:
           # Config README: https://github.com/korthout/backport-action#backport-action
+          auto_merge_enabled: true
           pull_description: |-
             Bot-based backport to `${target_branch}`, triggered by a label in #${pull_number}.