Update some environments to 3.10

Fixes #1603

tox.ini

@@ -456,7 +456,7 @@ commands =
   sphinx-build -E -a -W -b html -T . _build/html
 
 [testenv:spellcheck]
-basepython: python3.9
+basepython: python3.10
 recreate = True
 deps =
   codespell
@@ -465,7 +465,7 @@ commands =
   codespell
 
 [testenv:lint]
-basepython: python3.9
+basepython: python3.10
 recreate = False
 deps =
   -c dev-requirements.txt
@@ -537,7 +537,7 @@ commands =
   python scripts/eachdist.py lint --check-only
 
 [testenv:docker-tests]
-basepython: python3.9
+basepython: python3.10
 deps =
   pip >= 20.3.3
   pytest