♻️(backend) remove lazy from languages field on User model

The idea behind wrapping choices in `lazy` function was to allow
overriding the list of languages in tests with `override_settings`.
This was causin makemigrations to keep on including the field in
migrations when it is not needed. Since we finally don't override
the LANGUAGES setting in tests, we can remove it to fix the problem.

src/backend/core/models.py

@@ -24,7 +24,7 @@ from django.db import models, transaction
 from django.db.models.functions import Left, Length
 from django.template.loader import render_to_string
 from django.utils import timezone
-from django.utils.functional import cached_property, lazy
+from django.utils.functional import cached_property
 from django.utils.translation import get_language, override
 from django.utils.translation import gettext_lazy as _
 
@@ -244,7 +244,7 @@ class User(AbstractBaseUser, BaseModel, auth_models.PermissionsMixin):
 
     language = models.CharField(
         max_length=10,
-        choices=lazy(lambda: settings.LANGUAGES, tuple)(),
+        choices=settings.LANGUAGES,
         default=None,
         verbose_name=_("language"),
         help_text=_("The language in which the user wants to see the interface."),