ci: don't run FOSSA job in forks (#4285)

Author: erikgb

.github/workflows/scan.yaml

@@ -17,6 +17,8 @@ permissions:
 jobs:
   fossa:
     name: FOSSA
+    # FOSSA API key secret is not available in forks
+    if: github.secret_source != 'None'
     runs-on: ubuntu-latest
     steps:
       - name: Checkout