Revert "[doc] Run Sphinx 6 for creating documentation"

This reverts commit 27649f9ce273ed9486f2362310bd38827fbdcec4.

Reason for revert: T333816

Bug: T333816
Change-Id: Idc9f05baef36e282c13089247c054deb4a5a7a02
---
M tox.ini
1 file changed, 16 insertions(+), 2 deletions(-)

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

