`test_jax_bindings.py` fails if optional jax dependency is not available

[tvercaut]

The first line of this test is currenty to import jax:

torchsparsegradutils/torchsparsegradutils/tests/test_jax_bindings.py

Lines 1 to 15 in 3e13b3a

	import jax
	import numpy as np
	import pytest
	import torch
	from test_config import DEVICES
	import torchsparsegradutils as tsgu
	import torchsparsegradutils.jax as tsgujax
	# skip if JAX unavailable
	pytest.importorskip("jax")
	if not tsgujax.have_jax:
	pytest.skip("JAX bindings unavailable, skipping jax tests", allow_module_level=True)
	import jax.numpy as jnp

The import should be moved to after checking if jax is available.