Bring the dependencies in sync between `environment.yml` and `pyproject.toml`

[maresb]

I noticed that #346 updates the PyMC version in environment.yml but it doesn't make the corresponding change in pyproject.toml.

Also, there's an old numpy pin of <1.26.0 in environment.yml that I hope we can now get rid of.

I'll leave creating the PRs and testing to someone more involved.