chore: ensures that PR subjects start with lowercase (#427)

Fixes #425

.github/workflows/validate-semantic-pr.yml

@@ -10,7 +10,7 @@ defaults:
     shell: bash
 jobs:
   validate:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     steps:
       - name: Validate Pull Request
         uses: amannn/action-semantic-pull-request@v5.0.2
@@ -44,3 +44,13 @@ jobs:
           # merge commit, and it's easy to commit this by mistake. Enable this option
           # to also validate the commit message for one commit PRs.
           validateSingleCommit: true
+          # Configure additional validation for the subject based on a regex.
+          # This ensures the subject doesn't start with an uppercase character.
+          subjectPattern: ^(?![A-Z]).+$
+          # If `subjectPattern` is configured, you can use this property to override
+          # the default error message that is shown when the pattern doesn't match.
+          # The variables `subject` and `title` can be used within the message.
+          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.