In Django 4.2, `process_lhs()` is called for IsNull lookups,
which is how this bug came to appear. It was already there
and could be reproduced on Django 3.2.
The issue is when `LocalizedRef` is combined with a localized
lookup. The lookup is unaware of the existing localized ref
and adds another transform on top. This results in the
expression becoming:
```
field->'en'->'en'
```
* Support for Django 4
* Change pytest-django version
* Change psycopg2 version
* Change pytest version
* Change tox version
* Change pytest-cov version
* Update circle ci jobs
* Fix ci jobs
* Update ci to postgres 12
* Allow Django 5.0
* Bump Django min version to 3.2
* Fix CI to account for >= 3.2 requirement
* Fix quote
* Remove python 3.12 for now due to distutils removal
* Remove Django upper bound
* Add back python3.6,3.7 wfs
* Downgrade dj-database-url
* Fix isnull issue from Django 4
