tox: Bump minimum version to 4.x

'isolated_build' is no longer required since builds are isolated by
default in tox 4.

'basepython' is no longer required since tox 4 only supports Python 3
and 'basepython' defaults to the version of Python that tox is installed
with.

Signed-off-by: Stephen Finucane <[email protected]>

Author: stephenfin

tox.ini

@@ -1,7 +1,6 @@
 [tox]
-minversion = 2.4.0
+minversion = 4.2.0
 envlist = py{39,310,311,312}
-isolated_build = True
 
 [testenv]
 usedevelop = True
@@ -27,7 +26,6 @@ commands=
     python -X dev -X warn_default_encoding -m pytest --durations 25 {posargs}
 
 [testenv:docs]
-basepython = python3
 description =
     Build documentation.
 extras =
@@ -36,7 +34,6 @@ commands =
     sphinx-build -M html ./doc ./build/sphinx -W --keep-going
 
 [testenv:docs-live]
-basepython = python3
 description =
     Build documentation.
 extras =