fix pytest-python matrix

Author: youtux

tox.ini

@@ -1,7 +1,10 @@
 [tox]
 distshare = {homedir}/.tox/distshare
 envlist = py310-pytestlatest-linters,
-          py310-pytest{50,51,52,53,54,60,61,62,70,latest}-coverage,
+          ; python 3.10 is only supported by pytest >= 6.2.5:
+          py310-pytest{62,70,latest}-coverage,
+          ; the rest of pytest runs need to use an older python:
+          py39-pytest{50,51,52,53,54,60,61}-coverage,
           py{37,38,39}-pytestlatest-coverage,
           py310-pytestlatest-xdist-coverage
 skip_missing_interpreters = true