Throw detailed exception when error message could not be parsed

In some cases the schema does not match the response.
In this case it's not possible anymore to see what the original
error was. This is a quick fix to at least have some more sense
of why commercetools responded with an error.

Author: tleguijt

src/commercetools/client.py

@@ -3,6 +3,7 @@
 import warnings
 
 import requests
+from marshmallow.exceptions import ValidationError
 
 from commercetools.helpers import _concurrent_retry
 
@@ -102,7 +103,10 @@ def _process_error(self, response: requests.Response) -> None:
         # FIXME: The error response defined in the RAML should be used
         from commercetools.platform.models._schemas.error import ErrorResponseSchema
 
-        obj = ErrorResponseSchema().loads(response.content)
+        try:
+            obj = ErrorResponseSchema().loads(response.content)
+        except ValidationError:
+            raise Exception(f"Could not parse error response: {response.content}")
 
         # We'll fetch the 'raw' errors from the response because some of the
         # attributes are not included in the schemas.