doc: Do not use Sphinx 5.2.0.post0

Sphinx 5.2.0.post0 release has a known compatibility issue with the
`sphinx_rtd_theme` (see the issue readthedocs/sphinx_rtd_theme#1343).

Revert this commit once this compatibility issue is resolved.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>
1 file changed