[security-workflow] Fixed cron syntax (#2640)

Author: sreichel

.github/workflows/security-php.yml

@@ -1,9 +1,9 @@
-name: PHP Security Check
+name: "PHP Security Check"
 
 on:
   # Run automatically every Monday on midnight.
   schedule:
-    - '0 0 * * 1'
+    - cron: '0 0 * * 1'
   # Run on pull requests only when composer.lock has changed.
   pull_request:
     paths:
@@ -13,7 +13,7 @@ on:
 
 jobs:
   check:
-    runs-on: ubuntu-latest
+    runs-on: [ubuntu-latest]
 
     steps:
       - uses: actions/checkout@v3