Update Tox commands and environment list

Author: AA-Turner

tox.ini

@@ -1,33 +1,37 @@
 [tox]
+minversion = 2.4.0
 envlist =
-    py{36,37,38,39,310-dev},
+    py{38,39,310,311,312},
     flake8,
     mypy
-
-[gh-actions]
-python =
-    3.6: py36
-    3.7: py37
-    3.8: py38
-    3.9: py39
-    3.10: py310-dev
+isolated_build = True
 
 [testenv]
+usedevelop = True
+passenv =
+    https_proxy
+    http_proxy
+    no_proxy
+    COLORTERM
+    PERL
+    PERL5LIB
+    PYTEST_ADDOPTS
+    TERM
 deps=
     pytest
-    git+https://github.com/sphinx-doc/sphinx
+    sphinx @ git+https://github.com/sphinx-doc/sphinx
 extras=
     test
 setenv =
     PYTHONWARNINGS = all,ignore::DeprecationWarning:docutils.io
+    PYTEST_ADDOPTS = {env:PYTEST_ADDOPTS:} --color yes
 commands=
-    pytest --durations 25 {posargs}
+    python -X dev -X warn_default_encoding -m pytest --durations 25 {posargs}
 
 [testenv:flake8]
 description =
     Run style checks.
 extras =
-    test
     lint
 commands=
     flake8
@@ -36,7 +40,6 @@ commands=
 description =
     Run type checks.
 extras =
-    test
     lint
 commands=
     mypy sphinxcontrib/