tests/extmod/ujson_dump.py: Add test for dump to non-stream object.

tests/extmod/ujson_dump.py

@@ -16,3 +16,15 @@ print(s.getvalue())
 s = StringIO()
 json.dump({"a": (2, [3, None])}, s)
 print(s.getvalue())
+
+# dump to a small-int not allowed
+try:
+    json.dump(123, 1)
+except (AttributeError, OSError): # CPython and uPy have different errors
+    print('Exception')
+
+# dump to an object not allowed
+try:
+    json.dump(123, {})
+except (AttributeError, OSError): # CPython and uPy have different errors
+    print('Exception')