🚨(pylint) make pylint work and fix issues found

Pylint was not installed and wrongly configured. After making
it work, we fix all the issues found so it can be added to our
CI requirements.

src/backend/core/authentication.py

@@ -1,16 +1,13 @@
 """Authentication for the People core app."""
 from django.conf import settings
-from django.contrib.auth import get_user_model
 from django.utils.functional import SimpleLazyObject
 from django.utils.module_loading import import_string
-from django.utils.translation import get_supported_language_variant
 from django.utils.translation import gettext_lazy as _
 
 from drf_spectacular.authentication import SessionScheme, TokenScheme
 from drf_spectacular.plumbing import build_bearer_security_scheme_object
 from rest_framework import authentication
 from rest_framework_simplejwt.authentication import JWTAuthentication
-from rest_framework_simplejwt.exceptions import InvalidToken
 
 
 class DelegatedJWTAuthentication(JWTAuthentication):