ci: Fail on formatting issues

This lets the verible fail if there are any formatting issues reported.
This help to
- detect formatting issues soon (before opening a PR),
- clearly mark checks failed for uncompliant changes.

Signed-off-by: Nils Wistoff <[email protected]>

.github/workflows/verible.yml

@@ -3,8 +3,7 @@
 # SPDX-License-Identifier: Apache-2.0
 
 name: Verible
-on:
-  pull_request_target:
+on: [push, pull_request_target]
 
 jobs:
   format:
@@ -21,3 +20,4 @@ jobs:
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           files: 'core/**/*.{v,sv}'
+          fail_on_formatting_suggestions: true