fix pr url markdown

tool/lib/release_note_classes.dart

diff --git a/tool/lib/release_note_classes.dart b/tool/lib/release_note_classes.dart
index 2f4f233..4640d86 100644
--- a/tool/lib/release_note_classes.dart
+++ b/tool/lib/release_note_classes.dart
@@ -126,7 +126,7 @@
         final prNumber = match.namedGroup('pr_number');
         prUrls.add('[#$prNumber]($url)');
       }
-      markdown += ' - [](${prUrls.join(", ")})';
+      markdown += ' - ${prUrls.join(", ")}';
     }
 
     markdown += '\n';