chore: fix `require_trailing_commas` #2472

Job	Run time
examples (packages/flutter_bloc/example)	1m 5s
examples (examples/flutter_bloc_with_stream)	1m 19s
examples (examples/flutter_complex_list)	1m 22s
examples (examples/flutter_counter)	1m 22s
examples (examples/flutter_dynamic_form)	1m 41s
examples (examples/flutter_firebase_login)	4m 15s
examples (examples/flutter_form_validation)	59s
examples (examples/flutter_infinite_list)	1m 19s
examples (examples/flutter_login)	1m 40s
examples (examples/flutter_shopping_cart)	3m 46s
examples (examples/flutter_timer)	1m 20s
examples (examples/flutter_todos)	1m 47s
examples (examples/flutter_todos/packages/local_storage_todos_api)	1m 30s
examples (examples/flutter_todos/packages/todos_api)	1m 3s
examples (examples/flutter_todos/packages/todos_repository)	1m 2s
examples (examples/flutter_weather)	1m 36s
examples (examples/flutter_wizard)	58s
examples (examples/github_search/flutter_github_search)	1m 6s
build	0s
	29m 10s

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