ci: Skip pre-commit on branch builds

.github/workflows/linters.yml

@@ -55,6 +55,8 @@ jobs:
   linter:
     name: 'Frappe Linter'
     runs-on: ubuntu-latest
+    if: github.event_name == 'pull_request'
+
     steps:
       - uses: actions/checkout@v3
       - uses: actions/setup-python@v4