fix: update case to work with batch=1 and torch

Author: paquiteau

tests/operators/test_batch.py

@@ -235,8 +235,11 @@ def test_pinv_solver(operator, array_interface, image_data, kspace_data, optim):
     from mrinufft.extras.optim import loss_l2_reg
 
     img, res = operator.pinv_solver(
-        kspace_data, optim=optim, callback=loss_l2_reg, n_iter=10
+        kspace_data, optim=optim, callback=loss_l2_reg, n_iter=5
     )
 
     assert img.shape == operator.img_full_shape
-    assert res[0].size == operator.n_batchs
+    if operator.n_batchs > 1:
+        assert len(res[0]) == operator.n_batchs
+    else:
+        assert res[0].ndim == 0