[doc] Set sphinx version

1 job for main in 5 minutes and 52 seconds (queued for 1 second)
latest
Status Name Job ID Coverage
  Test
failed tox #1357747

00:05:52

49.0%
 
Name Stage Failure
failed
tox Test
150 files would be left unchanged.
___________________________________ summary ____________________________________
py39: commands succeeded
ERROR: lint: commands failed
sphinx: commands succeeded
coverage: commands succeeded
black: commands succeeded
Cleaning up file based variables
ERROR: Job failed: exit code 1