ci: enable pipeline runs on merge to main (#137)

Author: mstechly

.github/workflows/quality_checks.yaml

@@ -13,8 +13,11 @@
 # limitations under the License.
 
 name: Tests and quality checks
-on: [pull_request]
-
+on:
+  pull_request: 
+  push:
+    branches:
+      - main
 jobs:
   run_tests:
     runs-on: ubuntu-latest