Free (unpin) numpy so we can test with the new numpy 2.0.0 (needs Basemap update)

[valeriupredoi]

@ledm numpy=2.0.0 is fully out and released, it introduced a whole lot of breaking changes, so we should test with this branch; I'll have a first look at what tests break with it, then it'd be a very good idea if you took this branch and ran some of your standard analyses, see if anything breaks 🍺

• dependency roadblock: basemap >=1.3.6 is incompatible with numpy >=2 Numpy 2.0 Compatibility  matplotlib/basemap#604
• without basemap in, env solves well, and tests pass too: https://github.com/valeriupredoi/bgcval2/actions/runs/9663586030/job/26656099314?pr=133 (with the normal test error, that basemap module is not found)