semgrep on master only

.github/workflows/semgrep.yml

@@ -1,6 +1,5 @@
 name: Semgrep
 on:
-  pull_request: {}
   push:
     branches:
       - master
@@ -8,7 +7,6 @@ on:
 jobs:
   semgrep:
     name: Scan
-    if: "github.repository == 'polkadot-js/extension'"
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2