fix: use get_user_model()
Usage of get_user_model instead of User directly.
Compatibility with https://git.happy-dev.fr/startinblox/djangoldp-packages/djangoldp-account/#federation
Usage of get_user_model instead of User directly.
Compatibility with https://git.happy-dev.fr/startinblox/djangoldp-packages/djangoldp-account/#federation