chore: update failure conditions for docs workflow

[maxrjones]

We don't want PRs to show as failing CI due to this new docs job.

TODO:

• Add unit tests and/or doctests in docstrings
• Add docstrings and API docs for any new/modified user-facing classes and functions
• New/modified features documented in docs/user-guide/*.md
• Changes documented as a new file in changes/
• GitHub Actions have all passed
• Test coverage is 100% (Codecov passes)

[d-v-b]

if the docs build is allowed to pass even when this check fails, then maybe this check should not be in the same workflow as the docs build?

[maxrjones]

if the docs build is allowed to pass even when this check fails, then maybe this check should not be in the same workflow as the docs build?

I think eventually we would want the docs checking workflow to fail based on this test, once we clean up the state of our API so that the public functions only use public types. But for now, the noise is not worth it.