Past chat sessions can be made available for everyone to view

This test requires a chat with saved past chat sessions.

1. Prevent the student role from the capability "Read chat logs mod/chat:readlog" within the chat.
2. Log in as a teacher, update a chat activity and set 'Everyone can view past sessions' to Yes.
3. Log in as a student, access the chat and check that past chat sessions can be viewed via the 'View past chat sessions' link.
4. Log in as a teacher, update the chat activity and set 'Everyone can view past sessions' to No.
5. Check that past chat sessions can be viewed (as a teacher) via the 'View past chat sessions' link.
6. Log in as a student, access the chat and check that there is no longer a 'View past chat sessions' link.
7. Return the "Read chat logs mod/chat:readlog" capability to the student
8. Check that past chat sessions can be viewed (as a student) via the 'View past chat sessions' link.