Add link to issue

Author: greglittlefield-wf

test/over_react/component_declaration/builder_integration_tests/backwards_compatible/accessor_mixin_integration_test.dart

@@ -1,5 +1,6 @@
 //@dart=2.19
-// ^ Work around build issue on Dart 3 not allowing mixins of classes, due to pubspec 2.19 language version not being respected
+// ^ Work around build_web_compilers issue on Dart 3 not allowing mixins of classes, due to
+// pubspec's 2.19 language version not being respected: https://github.com/dart-lang/build/issues/4302
 // Copyright 2016 Workiva Inc.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");