ext: Update pybind11 to v2.8.1

Change-Id: Ia1c7081377f53fd470addf35526f8b28a949a7b0
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/52523
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Gabe Black <gabe.black@gmail.com>

ext/pybind11/tests/test_numpy_vectorize.py

@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 import pytest
+
 from pybind11_tests import numpy_vectorize as m
 
 np = pytest.importorskip("numpy")