Update actions yml

Author: zmsoft

.github/workflows/learn-github-actions.yml

@@ -35,7 +35,7 @@ jobs:
     - name: Merge PR
       run: |
         sleep 15
-        gh pr checkout 19 && git fetch origin master && git merge origin/master
+        gh pr checkout 20 && git fetch origin master && git merge --allow-unrelated-histories origin/master
         gh pr merge --squash --auto
       env:
         GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}