Fix failing test.

Author: rossbar

numpydoc/tests/test_docscrape.py

@@ -1497,6 +1497,8 @@ class Config():
         def __init__(self, a, b):
             self.numpydoc_xref_aliases = a
             self.numpydoc_xref_aliases_complete = b
+            # numpydoc.update_config fails if this config option not present
+            self.numpydoc_validation_checks = set()
 
     xref_aliases_complete = deepcopy(DEFAULT_LINKS)
     for key in xref_aliases: