Run Trivy scan on schedule instead of pull requests

Signed-off-by: Eddie Torres <torredil@amazon.com>

Author: torredil

.github/workflows/trivy.yaml

@@ -3,7 +3,8 @@ on:
   push:
     branches:
       - master
-  pull_request:
+  schedule:
+    - cron: '0 0 * * *'  # Run daily at midnight UTC
 jobs:
   build:
     name: Build