[Impeller] skip selectable text goldens for instability. (#143627)

Similar to other issues, appears that text goldens are really unstable with Impeller.

Part of flutter/flutter#143616

packages/flutter/test/widgets/selectable_text_test.dart

@@ -19,6 +19,7 @@ import 'package:flutter/rendering.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
 
+import '../impeller_test_helpers.dart';
 import '../widgets/clipboard_utils.dart';
 import '../widgets/editable_text_utils.dart' show textOffsetToPosition;
 import '../widgets/semantics_tester.dart';
@@ -5370,7 +5371,7 @@ void main() {
       find.byType(MaterialApp),
       matchesGoldenFile('selectable_text_golden.TextSelectionStyle.1.png'),
     );
-  });
+  }, skip: impellerEnabled); // https://github.com/flutter/flutter/issues/143616
 
   testWidgets('text selection style 2', (WidgetTester tester) async {
     await tester.pumpWidget(
@@ -5422,7 +5423,7 @@ void main() {
       find.byType(MaterialApp),
       matchesGoldenFile('selectable_text_golden.TextSelectionStyle.2.png'),
     );
-  });
+ }, skip: impellerEnabled); // https://github.com/flutter/flutter/issues/143616
 
   testWidgets('keeps alive when has focus', (WidgetTester tester) async {
     await tester.pumpWidget(