update tox testing

tox.ini

@@ -11,13 +11,13 @@
 # then then deleting compiled files has been found to fix it: `find . -name \*.pyc -delete`
 
 [tox]
-envlist = py39-sphinx5
+envlist = py311-sphinx5
 
 [testenv]
 usedevelop=true
 passenv = TERM  # To make terminal coloring / other variables pass through
 
-[testenv:py{37,38,39}-pre-commit]
+[testenv:py{311}-pre-commit]
 extras = code_style
 commands = pre-commit run {posargs}
 
@@ -43,7 +43,7 @@ deps =
 commands =
     stb serve docs --open-browser
 
-[testenv:py{37,38,39}-sphinx{5,6}]
+[testenv:py{311}-sphinx{5,6}]
 extras = test
 deps =
     sphinx5: sphinx>=5,<6