Update CanCanCan to only allow access to un-deleted classes

This commit changes the access rules in CanCanCan to prevent any user
(student, teacher or owner) from accessing deleted classes.

Author: fspeirs

app/models/ability.rb

@@ -62,7 +62,7 @@ def define_authenticated_non_student_abilities(user)
   def define_school_owner_abilities(school:)
     can(%i[read update destroy], School, id: school.id)
     can(%i[read], :school_member)
-    can(%i[read create import update destroy], SchoolClass, school: { id: school.id })
+    can(%i[read create import update destroy], SchoolClass, school: { id: school.id }, deleted: false)
     can(%i[read show_context], Project, school_id: school.id, lesson: { visibility: %w[teachers students] })
     can(%i[read create create_batch destroy], ClassStudent, school_class: { school: { id: school.id } })
     can(%i[read create destroy], :school_owner)
@@ -78,7 +78,7 @@ def define_school_teacher_abilities(user:, school:)
     can(%i[read], School, id: school.id)
     can(%i[read], :school_member)
     can(%i[create import], SchoolClass, school: { id: school.id })
-    can(%i[read update destroy], SchoolClass, school: { id: school.id }, teachers: { teacher_id: user.id })
+    can(%i[read update destroy], SchoolClass, school: { id: school.id }, teachers: { teacher_id: user.id }, deleted: false)
     can(%i[read create create_batch destroy], ClassStudent, school_class: { school: { id: school.id }, teachers: { teacher_id: user.id } })
     can(%i[read], :school_owner)
     can(%i[read], :school_teacher)
@@ -112,7 +112,7 @@ def define_school_student_abilities(user:, school:)
       ).select(:id)
     ).pluck(:id)
     can(%i[read], School, id: school.id)
-    can(%i[read], SchoolClass, school: { id: school.id }, students: { student_id: user.id })
+    can(%i[read], SchoolClass, school: { id: school.id }, students: { student_id: user.id }, deleted: false)
     # Ensure no access to ClassMember resources, relationships otherwise allow access in some circumstances.
     can(%i[read], Lesson, school_id: school.id, visibility: 'students', school_class: { students: { student_id: user.id } })
     can(%i[read create update], Project, school_id: school.id, user_id: user.id, lesson_id: nil, remixed_from_id: visible_lesson_project_ids)