Draft: Fix Schiller. Schiller vs Guo force test

Schiller needs shifted equilibrium velocity.

Test currently fails with deviations in the odd-order moments. No idea why. I think this test should pass.

lbmpy/forcemodels.py

@@ -199,6 +199,9 @@ class Schiller:
     def macroscopic_momentum_density_shift(self, density):
         return default_momentum_density_shift(self._force)
 
+    def equilibrium_velocity_shift(self, density):
+        return default_velocity_shift(density, self._force)
+
 
 class Buick:
     r"""