Enable CodeQL for pull requests (#374)

This reverts commit 1a04923.

Author: bandish-shah

.github/workflows/codeql-analysis.yml

@@ -14,6 +14,9 @@ name: "CodeQL"
 on:
   push:
     branches: [ main ]
+  pull_request:
+    # The branches below must be a subset of the branches above
+    branches: [ main ]
   schedule:
     - cron: '0 9 * * 1'  # Every Monday at 09:00 (9:00 AM)