chore: adjust pr-title check to enforce capitalization

Author: TwoFX

.github/workflows/pr-title.yml

@@ -15,6 +15,6 @@ jobs:
           script: |
             const msg = context.payload.pull_request? context.payload.pull_request.title : context.payload.merge_group.head_commit.message;
             console.log(`Message: ${msg}`)
-            if (!/^(feat|fix|doc|style|refactor|test|chore|perf): .*[^.]($|\n\n)/.test(msg)) {
+            if (!/^(feat|fix|doc|style|refactor|test|chore|perf): (?![A-Z][a-z]).*[^.]($|\n\n)/.test(msg)) {
               core.setFailed('PR title does not follow the Commit Convention (https://leanprover.github.io/lean4/doc/dev/commit_convention.html).');
             }