👷 Drop pull_request_target from commit checker

The job only reads commit messages, which works with the pull_request
trigger for PRs from forks too. Running it on both triggers checked every
PR twice, once with a privileged token it does not need.

Signed-off-by: David Barragán Merino <david.barragan@kaleidos.net>

.github/workflows/commit-checker.yml

@@ -7,13 +7,6 @@ on:
       - reopened
       - synchronize
       - ready_for_review
-  pull_request_target:
-    types:
-      - opened
-      - edited
-      - reopened
-      - synchronize
-      - ready_for_review
   push:
     branches:
       - main

.github/zizmor.yml

@@ -21,7 +21,6 @@ rules:
   dangerous-triggers:
     ignore:
       - auto-label.yml
-      - commit-checker.yml
   # Scope GitHub App tokens.
   github-app:
     ignore: