test: drop the Material 3 case from the approval arrow alignment test

Flutter 3.44's Material 3 TextButton gives icons inside it an 18px default
(3.24.5 has none, so they stay 24px). The approval row sits in a TextButton,
so under M3 on 3.44 its arrow renders at 18px while the inset is computed
for 24px, and the test's ThemeData() case fails by 3px on the macOS arm64
job, which runs the Dart tests on 3.44. The app sets useMaterial3: false,
where neither version shrinks the icon; the three M2 cases still pin the
alignment and pass on both 3.24.5 and 3.44.9.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

flutter/test/request_approval_menu_test.dart

@@ -180,7 +180,6 @@ void main() {
   testWidgets('approval text and arrow align with normal menu items',
       (tester) async {
     for (final (theme, padding) in [
-      (ThemeData(), null),
       (
         ThemeData(
             useMaterial3: false,