Update validate_secrets.yml

Validate_secrets.yml: run every 5 minutes on schedule

Stress-testing the Validate Secrets workflow with the 'Sync clock' workaround mentioned in https://github.com/actions/runner issue 2996 for errors like this:

'Authentication credentials are missing or invalid. - Provide a properly configured and signed bearer token, and make sure that it has not expired.'

.github/workflows/validate_secrets.yml

@@ -1,6 +1,10 @@
 name: 1. Validate Secrets
 run-name: Validate Secrets (${{ github.ref_name }})
-on: [workflow_call, workflow_dispatch]
+on:
+  workflow_call:
+  workflow_dispatch:
+  schedule:
+    - cron: '*/5 * * * *' # Runs every 5 minutes
 
 jobs:
   validate-access-token: