Select from Model.history, then use .instance, then chase a foreign key is broken

[jeking3]

Describe the bug
A clear and concise description of what the bug is.

In 3.1 HistoricForeignKey was introduced which is intended to work with Model.history.as_of(timepoint) and this works.

In 3.1.1, calling .instance on a historic record lookup does not populate _as_of which is necessary for HistoricForeignKey to work. You can query history with as_of(timepoint) and things work properly, but querying Model.history directly then converting to an instance cannot chase the foreign keys properly.

My workaround in another project:

            if isinstance(value, Value.history.model):
                # work around https://github.com/jazzband/django-simple-history/issues/983
                # queries beginning with as_of properly inject, but direct selections
                # converted to instances do not... :|  I missed something!!
                setattr(value, "_as_of", value.modified_at)
                # then value.instance properly works

[jeking3]

So I'm thinking the Historical model MAY have enough information in it to work without the extra attribute but I will have to play with it.

[jeking3]

In the end, if you did not query history with as_of, and you end up with a historical instance, if you call .instance on it, the HistoricalForeignKey chasers will use a fallback of the history_date of the record that made the instance when chasing relations! This was an easy fix and an easy win, and makes django-simple-history more powerful.