chore: update fossa.yml

Signed-off-by: Derek Su <derek.su@suse.com>

Author: derekbit

.github/workflows/fossa.yml

@@ -6,10 +6,6 @@ on:
       - v*
     tags:
       - v*
-  pull_request:
-    branches:
-      - master
-      - v*
   workflow_dispatch: {}
 
 permissions: {}