[doc] Run Sphinx 6 for creating documentation

Python 3.7 support was dropped with Sphinx 6.
Therefore use Python 3.9 to create documentation

Change-Id: Ibf3367f9abd1fb79133a56002a8c4e133de7967f
---
M tox.ini
1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/tox.ini b/tox.ini
index 17b9aca..f0ab1b4 100644
--- a/tox.ini
+++ b/tox.ini
@@ -83,7 +83,7 @@
 commands = {posargs}
 
 [testenv:doc]
-basepython = python3.7
+basepython = python3.9
 commands =
     sphinx-build -M html ./docs ./docs/_build -j auto
 deps =
@@ -100,7 +100,7 @@
     -rdocs/requirements.txt
 
 [testenv:sphinx]
-basepython = python3.7
+basepython = python3.9
 commands =
     sphinx-build -M html ./docs ./docs/_build -j auto -D html_theme=nature
 deps =

