I want to disable editing ALL objects within a particular TabularInline instance, while still allowing additions and while still allowing editing of the parent model.

I have this trivial setup:

```
class SuperviseeAdmin(admin.TabularInline):
  model = Supervisee

class SupervisorAdmin(admin.ModelAdmin):
  inlines = [SuperviseeAdmin]

admin.site.register(Supervisor, SupervisorAdmin)

```

I have tried adding a `has_change_permission` function to `SuperviseeAdmin` that returns `False` unconditionally, but it had no effect. 

I have tried setting `actions = None` in `SuperviseeAdmin` but it had no effect.

What might I be overlooking that could get this to work?