Use dict.get instead of getattr to retrieve user errors from Shopify request

The GraphQL library returns dict instead of object.

Closes #14964
(grafted from 4ec0ec9f0ae00251716f1e731c1d936857151fd9)

--HG--
branch : 8.0

modules/web_shop_shopify/tests/tools.py

@@ -41,7 +41,7 @@ def shopify_request(shop, query, variables=None, user_errors=None):
         names = user_errors.split('.')
         errors = result.data
         for name in names:
-            errors = getattr(errors, name, None)
+            errors = errors.get(name, None)
             if errors is None:
                 break
         if errors:

modules/web_shop_shopify/web.py

@@ -331,7 +331,7 @@ class Shop(metaclass=PoolMeta):
             names = user_errors.split('.')
             errors = result.data
             for name in names:
-                errors = getattr(errors, name, None)
+                errors = errors.get(name, None)
                 if errors is None:
                     break
             if errors: