ci(codeql): update CodeQL to only run on main branch and schedule (#53)

Author: erlendellefsen

.github/workflows/codeql.yml

@@ -6,11 +6,6 @@ on:
     paths:
       - "**.cs"
       - "**.csproj"
-  pull_request:
-    branches: [main]
-    paths:
-      - "**.cs"
-      - "**.csproj"
   schedule:
     - cron: "0 6 * * 1" # Monday 6am UTC