fix(flutter): 优化二级页面返回按钮样式

test/mine/settings_page_test.dart

@@ -54,7 +54,7 @@ void main() {
     expect(find.byKey(const Key('settings-page')), findsOneWidget);
     expect(
       tester.getSize(find.byKey(const Key('settings-back'))),
-      const Size(36, 36),
+      const Size(40, 40),
     );
     final title = tester.widget<Text>(find.byKey(const Key('subpage-title')));
     expect(title.style?.fontSize, 18);