Signup: use the recommended drf style for validation.

django_etesync/views.py

@@ -573,14 +573,12 @@ class AuthenticationViewSet(viewsets.ViewSet):
     @action_decorator(detail=False, methods=['POST'])
     def signup(self, request):
         serializer = AuthenticationSignupSerializer(data=request.data)
-        if serializer.is_valid():
+        serializer.is_valid(raise_exception=True)
         user = serializer.save()
 
         data = self.login_response_data(user)
         return Response(data, status=status.HTTP_201_CREATED)
 
-        return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)
-
     def get_login_user(self, serializer):
         username = serializer.validated_data.get('username')
         email = serializer.validated_data.get('email')