sync_settings_ui: assert the password form starts collapsed when Google is offered

Flagged during todo's migration: the "Google available" test asserted the
button renders and works, but never checked that the password/email
ExpansionTile actually starts collapsed behind it (initiallyExpanded:
!googleAvailable) -- the one behavior the old duplicated todo test covered
that this package's own suite didn't.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KdSp6Nbrs9xvsWkCMDN9a1

sync_settings_ui/test/sync_settings_screen_test.dart

@@ -190,6 +190,13 @@ void main() {
         await tester.pumpAndSettle();
 
         expect(find.text('Sign in with Google'), findsOneWidget);
+        // The password form is collapsed behind its ExpansionTile when
+        // Google is offered -- only the field labels prove that; the tile's
+        // own title text is present either way.
+        expect(
+          find.widgetWithText(TextField, 'Sync account email'),
+          findsNothing,
+        );
         await tester.tap(find.text('Sign in with Google'));
         await tester.pumpAndSettle();