github-actions: Don't run code scanning workflow every week.

Since we already run this on every push we don't need to run it as a
cron job every week for no reason. While we are touching this code
block, we convert it to on: [push, pull_request] since the previous
format felt weird. It was only written that way because we had the
cron job declared there.

.github/workflows/codeql-analysis.yml

@@ -1,10 +1,6 @@
 name: "Code Scanning"
 
-on:
-  push:
-  pull_request:
-  schedule:
-    - cron: '0 5 * * 1'
+on: [push, pull_request]
 
 jobs:
   CodeQL: