Reformat src/docs/src/conf.py

After a recent change [1], python black started to complain. Since we updated
docs only in that PR we skipped the python black check. So reformat to make the
checker happy.

In the future make sure to run python black formatting even when we make
docs-only changes.

[1] https://github.com/apache/couchdb/pull/4208
2 files changed