install the dev version of sparse in the upstream-dev CI

[keewis]

sparse issued a release yesterday, which seems to break one of our tests (numpy.allcose on a ndarray and COO is not implemented). This enables installing the dev version of sparse in the upstream-dev CI, and I'm planning to either xfail or fix the failing test here.

Edit: I can reproduce the failure with sparse=0.11.2 so that's not the reason for the failing test... that's wrong, a new environment downgraded to sparse=0.11.2 will not fail, but upgrading will introduce the failure again.

• Passes pre-commit run --all-files

[keewis]

the reason for the failure seems to be that for sparse=0.11.2 dense_var.where(sparse_var) returns dense while for sparse=0.12 it returns sparse. We can fix that by casting ret_d.data to dense if it exists and is sparse:

    if isinstance(ret_d, xr.Variable) and isinstance(ret_d.data, sparse.SparseArray):
        ret_d = ret_d.copy(data=ret_d.data.todense())

but we can probably figure out a better way to compare dense and sparse arrays.

[keewis]

since the sparse (and pint) tests will eventually be superseded by #4972, we can skip finding a better way to compare sparse and dense arrays. I'll merge now to fix the CI in other PRs.