fix: update expected value for unit test on Attack of the Trolls

One of the test case for the 4th task of the exercise Attack of the Trolls had a wrong expected case.
Specifically the test case Check_all_for_read_and_write() should have Permission.All as expected value instead of Permission.Read | Permission.Write.

(cc @ErikSchierboom)

Good catch! I’ve merged your PR. Thanks.