Docs build is broken

[tswast]

I'm getting the following error when I try to build the docs.

Warning, treated as error:
/var/code/gcp/docs/trace/index.rst:22:failed to import google.cloud.gapic.trace.v1.trace_service_client
nox > Command bash ./test_utils/scripts/update_docs.sh failed with exit code 1
nox > Session docs failed. :(
Exited with code 1

This is also causing builds to fail for all PRs. I believe this was caused by #4379