Failing test due to recent Guo force model changes

Ever since the Guo force model has been updated (see !476 (merged)), the test SuViscoelasticityLongTest fails. It uses the Guo field force model and compares the steady-state solution against a reference velocity. The used LBM model seems to update the force field in every time step (https://i10git.cs.fau.de/walberla/walberla/-/blob/master/src/lbm/SuViscoelasticity.h#L229).

The failing test might hint towards possible problems either with the reference solution of this test as it might be tailored to the previous force model (unfortunately no more info about the source is given) or with the newly introduced changes in the Guo force model.