Remove unnecessary quotes from the CodeQL workflow

We generally prefer to only use quotes when either necessary due to
content or when we want to force string conversion.

.github/workflows/codeql-analysis.yml

@@ -20,7 +20,7 @@ on:
     branches-ignore:
       - dependabot/**
   schedule:
-    - cron: '0 21 * * 6'
+    - cron: 0 21 * * 6
 
 jobs:
   diagnostics: