Python 3.12 everywhere

tox.ini

@@ -26,7 +26,7 @@ commands =
     {envbindir}/trial {posargs:treq}
 
 [testenv:mypy]
-basepython = python3.8
+basepython = python3.12
 deps =
     mypy==1.0.1
     mypy-zope==0.9.1
@@ -38,27 +38,27 @@ commands =
         {posargs:src}
 
 [testenv:flake8]
-python = python3.11
+python = python3.12
 skip_install = True
 deps = flake8
 commands = flake8 src/treq/
 
 [testenv:towncrier]
-python = python3.11
+python = python3.12
 deps =
     towncrier
 commands =
     towncrier {posargs:--draft}
 
 [testenv:twine]
-python = python3.11
+python = python3.12
 deps =
     twine
 commands =
     twine check {distdir}/*.*
 
 [testenv:check-manifest]
-python = python3.11
+python = python3.12
 deps =
     check-manifest
 commands =
@@ -67,7 +67,7 @@ commands =
 [testenv:docs]
 extras = docs
 changedir = docs
-basepython = python3.8
+basepython = python3.12
 commands =
     sphinx-build -b html . html