Fix CI workflow configuration (#67)

Author: mgruner

.github/workflows/ci.yml

@@ -3,6 +3,8 @@ on:
   push:
     branches: [master]
   pull_request:
+    branches:
+      - master
   schedule:
     # Run every on Friday to ensure everything works as expected.
     - cron:  '0 6 * * 5'