ci: disable job for bot pushes

Author: Genyus

.github/workflows/classroom-autograding.yml

@@ -11,6 +11,7 @@ env:
 jobs:
   autograding:
     runs-on: ubuntu-latest
+    if: github.event.sender.type != 'Bot'
     steps:
       - name: Checkout grading repo
         uses: actions/checkout@v4