Add ignore for Dart Code Metrics lint (#10070)

"this getter is used but never assigned a value"

packages/devtools_app/lib/src/screens/inspector/layout_explorer/ui/layout_explorer_widget.dart

diff --git a/packages/devtools_app/lib/src/screens/inspector/layout_explorer/ui/layout_explorer_widget.dart b/packages/devtools_app/lib/src/screens/inspector/layout_explorer/ui/layout_explorer_widget.dart
index d1392f2..e46cf2b 100644
--- a/packages/devtools_app/lib/src/screens/inspector/layout_explorer/ui/layout_explorer_widget.dart
+++ b/packages/devtools_app/lib/src/screens/inspector/layout_explorer/ui/layout_explorer_widget.dart
@@ -49,9 +49,11 @@
 
   InspectorObjectGroupManager? objectGroupManager;
 
+  // ignore: unused-code, false positive "this getter is used but never assigned a value"
   AnimatedLayoutProperties<L>? get animatedProperties => _animatedProperties;
   AnimatedLayoutProperties<L>? _animatedProperties;
 
+  // ignore: unused-code, false positive "this getter is used but never assigned a value"
   L? get properties =>
       _previousProperties ?? _animatedProperties as L? ?? _properties;