style(ui): shorten update button label to Update

The shared newVersionUpdate label now reads Update on the app upgrade
dialog, the tracker update button and the extension update dialog, so
the extension flow matches the host dialog wording.

ui/flutter/test/widget_test.dart

@@ -2329,7 +2329,7 @@ void main() {
     final progress = find.descendant(of: updateButton, matching: find.byType(shad.CircularProgressIndicator));
     expect(progress, findsOneWidget);
     expect(tester.getSize(progress), const Size.square(14));
-    expect(find.descendant(of: updateButton, matching: find.text('Update Now')), findsOneWidget);
+    expect(find.descendant(of: updateButton, matching: find.text('Update')), findsOneWidget);
 
     runtimeController.completeTrackerUpdate();
     await tester.pumpAndSettle();