docfx session does not run for python-spanner-django

[dandhlee]

Noticed this on #767, not sure what could be wrong. Will investigate.

[IlyaFaer]

@dandhlee, I've investigated it a bit. The problem is happening for this class:

python-spanner-django/django_spanner/base.py

Line 22 in 7312906

class DatabaseWrapper(BaseDatabaseWrapper):

I've added try-except into docfx function to log what's happening there, see this:

So, source wasn't built for the class DatabaseWrapper

[dandhlee]

Ah, I think the bigger issue is that it's using Sphinx V5, which has a loooot of breaking changes. I'll pin to use Sphinx v4.