Lesson group overrides should show a warning if the activity is hidden.

The lesson's user overrides shows a warning when the activity is hidden. However, it does not happens the same with the group overrides.

How to reproduce:

1. Create a course with some users and groups (with only students in the groups)
2. Create a lesson activity with som availability like a password and a future date "available from"
3. Access the activity and go to "overrides"
4. Add a user override altering some of the restriction for a specific user
5. Add a group override altering some of the restrictions for a specific group
6. Hide the activity to the students
7. Go to the lesson user overrides:
   1. Check the user override has an * indicating: "This override is inactive because the user's access to the activity is restricted. This can be due to group or role assignments, other access restrictions, or the activity being hidden."
8. Go to the lesson group override:
   1. Expected: the group override has a warning indicating that the activity access may be restricted for some group users.
   2. What happens: there is no warning at all