ci: add better message for PR subject pattern error

.github/workflows/pr-title.yml

@@ -71,6 +71,10 @@ jobs:
 
           # Disallow uppercase letters at the beginning of the subject
           subjectPattern: ^(?![A-Z]).+$
+          subjectPatternError: |
+            The subject "{subject}" found in the pull request title "{title}"
+            didn't match the configured pattern. Please ensure that the subject
+            doesn't start with an uppercase character.
 
       - uses: marocchino/sticky-pull-request-comment@v2
         # When the previous steps fails, the workflow would stop. By adding this