PointerSignalKind forwards-compatibility (#106906)

diff --git a/packages/flutter/lib/src/gestures/converter.dart b/packages/flutter/lib/src/gestures/converter.dart
index 34c278c..1e00d68 100644
--- a/packages/flutter/lib/src/gestures/converter.dart
+++ b/packages/flutter/lib/src/gestures/converter.dart
@@ -263,6 +263,8 @@
                 embedderId: datum.embedderId,
               );
             case ui.PointerSignalKind.unknown:
+            default: // ignore: no_default_cases, to allow adding a new [PointerSignalKind]
+                     // TODO(moffatman): Remove after landing https://github.com/flutter/engine/pull/34402
               // This branch should already have 'unknown' filtered out, but
               // we don't want to return anything or miss if someone adds a new
               // enumeration to PointerSignalKind.