diff_against does not detect changes on deletion history type

[euriostigue]

Describe the bug
I am comparing two records:

• The record describing when the object was created
• The record describing when the object was deleted

When I use diff_against between these two records, the returned ModelDelta has an empty changes list.

To Reproduce

In [21]: person = Person.objects.create(name="Eric")

In [22]: person_pk = person.id

In [23]: person.delete()
Out[23]: (1, {'data.Person': 1})

In [24]: records = HistoricalPerson.objects.filter(id=person_pk)

In [25]: records
Out[25]: <QuerySet [<HistoricalPerson: Person object (4) as of 2024-02-14 21:13:19.406277+00:00>, <HistoricalPerson: Person object (4) as of 2024-02-14 21:13:02.534529+00:00>]>

In [26]: delta = records[0].diff_against(records[1])

In [27]: delta.__dict__
Out[27]: 
{'changes': [],
 'changed_fields': [],
 'old_record': <HistoricalPerson: Person object (4) as of 2024-02-14 21:13:02.534529+00:00>,
 'new_record': <HistoricalPerson: Person object (4) as of 2024-02-14 21:13:19.406277+00:00>}

In [28]: delta.new_record.history_type
Out[28]: '-'

Expected behavior
I expect to see that all values have changed to None because the record no longer exists.

Environment (please complete the following information):

• OS: MacOS Sonoma 14.2.1
• Browser (if applicable): Chrome
• Django Simple History Version: 3.4.0
• Django Version: 5.0.2
• Database Version: Postgres 13

Additional context
After reading the diff_against implementation, it appears like history_type is not considered. Instead, changes are computed by checking field value differences:

            if old_value != current_value:
                changes.append(ModelChange(field, old_value, current_value))
                changed_fields.append(field)