[physics] Fix make_incompressible() for FVM

phi/physics/fluid.py

@@ -172,7 +172,7 @@ def make_incompressible(velocity: Field,
         wide_stencil = not velocity.is_staggered
     pressure = math.solve_linear(masked_laplace, div, solve, velocity.boundary, hard_bcs, active, wide_stencil=wide_stencil, order=order, implicit=None, upwind=None, correct_skew=correct_skew)
     # --- Subtract grad p ---
-    grad_pressure = field.spatial_gradient(pressure, input_velocity.extrapolation, at=velocity.sampled_at, order=order)
+    grad_pressure = field.spatial_gradient(pressure, input_velocity.extrapolation, at=velocity.sampled_at, order=order, scheme='green-gauss')
     if hard_bcs is not None:
         grad_pressure *= hard_bcs
     velocity = (velocity - grad_pressure).with_extrapolation(input_velocity.extrapolation)