Fix CI: Add workflow_call trigger to security-scan workflow (#2008)

The security-scan.yml workflow was missing the workflow_call trigger
needed to make it reusable. This was causing the run-on-pr.yml workflow
to fail when trying to call it.

Added workflow_call trigger while preserving existing triggers for
workflow_dispatch, push, pull_request, and scheduled runs.

Author: JAORMX

.github/workflows/security-scan.yml

@@ -1,6 +1,7 @@
 name: Security Scan
 
 on:
+  workflow_call:
   workflow_dispatch:
   push:
     branches: [ main ]