[scenic_flutter] Migrating deprecated method 1/2

This places a lint ignore in preparation of migrating deprecated code.
The method that is currently being overridden will be removed, which will break
analysis. Having this lint in place will allow us to remove the method without breaking,
and then follow-up in another change to remove the `@override` once completed.

Flutter PR to remove the deprecated method: https://github.com/flutter/flutter/pull/73749

Change-Id: I1dcb5ed461c4f4165d52852634a736482bcd3c18
Reviewed-on: https://fuchsia-review.googlesource.com/c/topaz/+/470861
Commit-Queue: Auto-Submit <auto-submit@fuchsia-infra.iam.gserviceaccount.com>
Reviewed-by: David Worsham <dworsham@google.com>
Reviewed-by: Jaeheon Yi <jaeheon@google.com>
Fuchsia-Auto-Submit: Kate Lovett <katelovett@google.com>
diff --git a/public/dart/fuchsia_scenic_flutter/lib/src/child_view_render_box.dart b/public/dart/fuchsia_scenic_flutter/lib/src/child_view_render_box.dart
index de437d5..0880f23 100644
--- a/public/dart/fuchsia_scenic_flutter/lib/src/child_view_render_box.dart
+++ b/public/dart/fuchsia_scenic_flutter/lib/src/child_view_render_box.dart
@@ -188,7 +188,9 @@
   S find<S>(Offset regionOffset) => null;
 
   @override
-  Iterable<S> findAll<S>(Offset regionOffset) => <S>[];
+  Iterable<S> findAll<S>(Offset regionOffset) { // ignore: override_on_non_overriding_member
+    return <S>[];
+  }
 
   @override
   bool findAnnotations<S>(AnnotationResult<S> result, Offset localPosition,