make sure version check includes hotfixes (#33459)

dev/bots/test.dart

@@ -673,7 +673,7 @@ Future<void> _verifyVersion(String filename) async {
     print('$redLine');
     exit(1);
   }
-  final RegExp pattern = RegExp(r'^[0-9]+\.[0-9]+\.[0-9]+(-pre\.[0-9]+)?$');
+  final RegExp pattern = RegExp(r'^\d+\.\d+\.\d+(?:|-pre\.\d+|\+hotfix\.\d+)$');
   if (!version.contains(pattern)) {
     print('$redLine');
     print('The version logic generated an invalid version string.');