ci: trigger differential-shellcheck workflow on push

Fixes: redhat-plumbers-in-action/differential-shellcheck#215

.github/workflows/lint.yml

@@ -2,6 +2,8 @@
 
 name: Lint
 on:
+  push:
+    branches: [master]
   pull_request:
     branches: [master]
 
@@ -12,6 +14,9 @@ jobs:
   shellcheck:
     runs-on: ubuntu-latest
 
+    permissions:
+      security-events: write
+
     steps:
       - name: Repository checkout
         uses: actions/checkout@v3