Use sysconfig instead of distutils for Python 3.10 compatability (#2100)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: 9999years

docs/changelog/2100.misc.rst

@@ -0,0 +1,2 @@
+``tox`` no longer shows deprecation warnings for ``distutils.sysconfig`` on
+Python 3.10 - by :user:`9999years`

src/tox/helper/get_site_package_dir.py

@@ -1,8 +1,8 @@
 from __future__ import unicode_literals
 
-import distutils.sysconfig
 import json
 import sys
+import sysconfig
 
-data = json.dumps({"dir": distutils.sysconfig.get_python_lib(prefix=sys.argv[1])})
+data = json.dumps({"dir": sysconfig.get_path("purelib", vars={"base": sys.argv[1]})})
 print(data)