Avoid sphinx 6.x for now

cderici · cderici · commit 4e1ca3c7016b · 2023-07-10T13:28:37.000-06:00
As it turns out that the sphinx &gt;=6.x doesn't play well with
coroutines.
diff --git a/docs/requirements.txt b/docs/requirements.txt
@@ -1,6 +1,6 @@
 pytz
 pymacaroons
-sphinx
+sphinx==5.3.0
 sphinxcontrib-asyncio
 sphinx_rtd_theme
 websockets
