Ensure all items of array are checked for uniqueness

Fix bug where the function would return (True) early if the first two items of
the array are unique, preventing verification of other array items.

jsonschema/_utils.py

@@ -188,7 +188,8 @@ def uniq(container):
         sliced = itertools.islice(sort, 1, None)
 
         for i, j in zip(sort, sliced):
-            return not _sequence_equal(i, j)
+            if _sequence_equal(i, j):
+                return False
 
     except (NotImplementedError, TypeError):
         seen = []