docs: fix typo in `compass_app` `BookingSummary` class doc (#2786)

Fixes a [typo] in the [`compass_app`] sample's [`booking_summary.dart`].
The class doc for the `BookingSummary` class had "activities" written as
"activitities".


[`compass_app`]:
https://github.com/flutter/samples/tree/main/compass_app
[`booking_summary.dart`]:
https://github.com/flutter/samples/blob/main/compass_app/app/lib/domain/models/booking/booking_summary.dart
[typo]:
7abc7b91f2/compass_app/app/lib/domain/models/booking/booking_summary.dart (L12C10-L12C22)

Fixes #2785 .

compass_app/app/lib/domain/models/booking/booking_summary.dart

@@ -9,7 +9,7 @@ part 'booking_summary.g.dart';
 
 /// BookingSummary contains the necessary data to display a booking
 /// in the user home screen, but lacks the rest of the booking data
-/// like activitities or destination.
+/// like activities or destination.
 ///
 /// Use the [BookingRepository] to obtain a full [Booking]
 /// using the [BookingSummary.id].