Log Message:
py-django-treebeard: updated to 4.5.1

Release 4.5.1

Removed unnecessary default in MP's depth field.

Release 4.5

Add support for custom primary key fields with custom names.
Add support for Python 3.9.
Add support for MSSQL 2019.
Add Code of conduct
Removed outdated Sqlite workaround code
Remove last remains of Python 2.7 code
Use Pytest-django and fixtures for testing