[pytype] Disable mypy type checking on third_party/markeupsafe target

Change-Id: Ie56dc96d387784a98e3d30f97fb2ae5dd79b0fcb
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/markupsafe/+/1116439
Reviewed-by: Danny Rosen <dannyrosen@google.com>
Reviewed-by: Kevin Cho <chok@google.com>