tools/mpy-tool.py: Ignore linter failure in Python 2 compatibility code.

Found by Ruff checking F821.

Signed-off-by: Angus Gratton <angus@redyak.com.au>

tools/mpy-tool.py

@@ -35,7 +35,7 @@
     bytes_cons = lambda val, enc=None: bytearray(val)
     is_str_type = lambda o: isinstance(o, str)
     is_bytes_type = lambda o: type(o) is bytearray
-    is_int_type = lambda o: isinstance(o, int) or isinstance(o, long)
+    is_int_type = lambda o: isinstance(o, int) or isinstance(o, long)  # noqa: F821
 
     def hexlify_to_str(b):
         x = hexlify_py2(b)