Fix GetMixin to let it return an ApiObject

Fix `transip.mixins.GetMixin` by letting it return a
`transip.base.ApiObject` instead of a dictionary.

Signed-off-by: Roald Nefs <info@roaldnefs.com>

Author: roaldnefs

transip/mixins.py

@@ -42,7 +42,9 @@ def get(self, id: str, **kwargs) -> Optional[Type[ApiObject]]:
                 path=self._path,
                 id=id
             )
-            obj: Type[ApiObject] = self.client.get(path)[self._resp_get_attr]
+            obj: Type[ApiObject] = self._obj_cls(  # type: ignore
+                self.client.get(path)[self._resp_get_attr]
+            )
             return obj
         return None