Fix issues with tox 4.2.4

tox now hard fails if there is mismatch in spec
attributes[1]. This works around the issue
temporarily. We probably have to drop py38 jobs
and specify basepython for py39 target in the
future.

[1] tox-dev/tox#2824

Closes-Bug: #2002035
Change-Id: I4256a51afd011048eaaaf5d3c225ab36f75708ed

tox.ini

@@ -1,6 +1,7 @@
 [tox]
 minversion = 3.18.0
 envlist = pep8,py,tht
+ignore_base_python_conflict = True
 
 [testenv]
 basepython = python3