Explicitly include all fields in test schema to avoid deprecation war…

…ning

Otherwise we encounter this warning:

```
graphene/utils/subclass_with_meta.py:46: DeprecationWarning: Creating a DjangoObjectType without either the `fields` or the `exclude` option is deprecated. Add an explicit `fields = '__all__'` option on DjangoObjectType User to use all fields
    super_class.__init_subclass_with_meta__(**options)
```

tests/schema.py

@@ -12,16 +12,19 @@
 class Project(DjangoObjectType):
     class Meta:
         model = models.Project
+        fields = "__all__"
 
 
 class Expense(DjangoObjectType):
     class Meta:
         model = models.Expense
+        fields = "__all__"
 
 
 class User(DjangoObjectType):
     class Meta:
         model = UserModel
+        fields = "__all__"
 
 
 # Queries