Fix tests after recent M3 demo changes (#2194)

It's not yet clear to me what in
e5f3bacaf8
is causing the failure, but this resolves it.

material_3_demo/test/component_screen_test.dart

@@ -110,8 +110,9 @@ void main() {
     expect(find.byType(FilterChip), findsNWidgets(2));
     expect(find.byType(InputChip), findsNWidgets(2));
 
-    // Date pickers
-    expect(find.widgetWithText(TextButton, 'Show date picker'), findsOneWidget);
+    // Date and time pickers
+    expect(find.widgetWithText(DatePicker, 'Show date picker'), findsOneWidget);
+    expect(find.widgetWithText(TimePicker, 'Show time picker'), findsOneWidget);
 
     // Menus
     expect(find.byType(MenuAnchor), findsNWidgets(5));
@@ -128,9 +129,6 @@ void main() {
     // Switches
     expect(find.byType(Switch), findsNWidgets(4));
 
-    // Time pickers
-    expect(find.widgetWithText(TextButton, 'Show time picker'), findsOneWidget);
-
     // TextFields
     expect(find.widgetWithText(TextField, 'Disabled'), findsNWidgets(2));
     expect(find.widgetWithText(TextField, 'Filled'), findsNWidgets(2));