Fix union test.

The old test was just testing the same thing twice. Replace the second test with a
different one.

Author: desert

tests/test_make.py

@@ -236,8 +236,8 @@ class A:
 
     assert schema.dump(loaded) == dumped
 
-    dumped = {"x": "X"}
-    loaded = A("X")
+    dumped = {"x": 5}
+    loaded = A(5)
 
     assert schema.load(dumped) == loaded
     assert schema.dump(loaded) == dumped