github-action: Add AsciiDoc freeze warning

Author: reakaleek

.github/workflows/comment-on-asciidoc-changes.yml

@@ -2,7 +2,8 @@
 name: Comment on PR for .asciidoc changes
 
 on:
-  pull_request:
+  # We need to use pull_request_target to be able to comment on PRs from forks
+  pull_request_target:
     types:
       - synchronize
       - opened