Unpin numpy version

[jobrachem]

See this comment:

#198 (comment)

The issue in the CI does not originate from scipy, but instead from incompatibility of tensorflow probability to numpy 2.0. At first, I could not reproduce the issue locally, because locally, I installed using the pmc specs, and pymc currently pins to numpy<2.

The current solution is to pin numpy in liesel to <2.0, too, until the downstream issue is addressed. There's already an issue in the tensorflow probability repo:

• MultivariateNormal* constructor crashes with Numpy 2.0  tensorflow/probability#1814

Once this is addressed, we can unpin numpy, since pymc correctly handles its dependency on numpy itself.

Originally posted by @jobrachem in #198 (comment)