[Python-modules-team] Bug#961206: improve sphinx usage for cross building

[Drew Parsons]

Source: sphinx
Followup-For: Bug #961206

I've just updated numba from Build-Depends: python3-sphinx
to Build-Depends: sphinx as recommended here (#961741).

The change is giving me a lintian error:

E: numba source: missing-build-dependency-for-dh-addon sphinxdoc => python-sphinx | python3-sphinx | dh-sequence-sphinxdoc


Should the lintian test be updated for the new sphinx structure (e.g.
to include sphinx as an alternative)?