Fix https://sentry.lil.school/lil/backend/issues/11/

(cherry picked from commit 5b22c5c)

apps/auth/views.py

@@ -37,8 +37,7 @@ class LearnerRegistrationView(FormView):
         password = form.cleaned_data['password']
 
         user, created = User.objects.get_or_create(
-            username=email, email=email,
-            first_name=first_name, last_name=last_name
+            email=email,
         )
 
         if not created:
@@ -47,6 +46,10 @@ class LearnerRegistrationView(FormView):
                 'errors': {'__all__': [{'message': 'Возможно вы уже зарегистрированы?'}]}
             }, status=400)
 
+        user.username = email
+        user.first_name = first_name
+        user.last_name = last_name
+
         user.set_password(password)
         user.save()
         login(self.request, user)