Clean up some dead interpreters in tox

tox.ini

@@ -12,7 +12,6 @@ looponfailroots =
 # Keep docs in sync with docs env and .readthedocs.yml.
 [gh-actions]
 python =
-    3.6: py36, py36-numpy
     3.7: py37, py37-numpy
     3.8: py38, py38-numpy
     3.9: py39, py39-numpy, lint, manifest, typing, changelog, docs
@@ -23,7 +22,7 @@ python =
 
 
 [tox]
-envlist = typing,lint,py36{,-numpy},py37{,-numpy},py38{,-numpy},py39{,-numpy},py310{,-numpy},pypy{,-numpy},pypy3{,-numpy},manifest,docs,pypi-description,changelog,coverage-report
+envlist = typing,lint,py37{,-numpy},py38{,-numpy},py39{,-numpy},py310{,-numpy},pypy{,-numpy},pypy3{,-numpy},manifest,docs,pypi-description,changelog,coverage-report
 isolated_build = True
 
 
@@ -36,14 +35,6 @@ extras = {env:TOX_AP_TEST_EXTRAS:tests}
 commands = python -m pytest {posargs}
 
 
-[testenv:py27]
-extras = {env:TOX_AP_TEST_EXTRAS:tests}
-commands = coverage run -m pytest {posargs}
-
-[testenv:py36-numpy]
-extras = tests-numpy
-commands = python -m pytest {posargs}
-
 [testenv:py37-numpy]
 extras = tests-numpy
 commands = python -m pytest {posargs}
@@ -108,15 +99,15 @@ extras = {env:TOX_AP_TEST_EXTRAS:tests}
 commands = coverage run -m pytest {posargs}
 
 [testenv:coverage-report]
-basepython = python3.9
+basepython = python3.11
 skip_install = true
 deps = coverage[toml]>=5.0.2
 commands =
     coverage combine
     coverage report
 
 [testenv:lint]
-basepython = python3.9
+basepython = python3.11
 skip_install = true
 deps =
     pre-commit
@@ -127,7 +118,7 @@ commands =
 
 [testenv:docs]
 # Keep basepython in sync with gh-actions and .readthedocs.yml.
-basepython = python3.9
+basepython = python3.11
 extras = docs
 commands =
     sphinx-build -n -T -b html -d {envtmpdir}/doctrees doc doc/_build/html