Make tests run on the latest version of jax

[Michael-T-McCann]

Thanks to #73, SCICO depends on a specific jax version which won't always be the latest one. In order to spot compatibility changes coming down the pike and to help us keep up with jax, we could make the CI run tests with both the pinned jax version and the current latest jax version.

Links from Luke:

• see here: https://docs.github.com/en/actions/learn-github-actions/managing-complex-workflows#using-a-build-matrix
• for concrete example of setting up a build matrix, see https://github.com/google/jax/blob/main/.github/workflows/ci-build.yaml

[lukepfister]

this is a great idea. jax moves fast and there are frequently breaking changes. it's not easy to spot them coming unless you check the jax issue tracker very frequently.