fix: work around poetry hanging trying to run poetry lock

Currently trying to create a new project from the boilerplate or to
update an existing one causes poetry to sit in an infinite loop. The
root cause is covered in an [issue elsewhere][1] and will be resolved
when the pending version of google-auth [is released][2].

Temporarily work around the issue until [1] is resolved.

[1]: https://gitlab.developers.cam.ac.uk/uis/devops/infra/
      gitlab-bots-deployment/-/issues/51
[2]: https://github.com/googleapis/google-auth-library-python/pull/1797