nsinker_spherical_shell convergence issues

[tjhei]

But nsinker_spherical_shell cannot converge using gmg, and amg doesn't converge either.

Additional information: 
    The iterative Stokes solver in
    StokesMatrixFreeHandlerImplementation::solve did not converge.

    The initial residual was: 1.000758e-02
    The final residual is: 1.745499e-08
    The required residual for convergence is: 1.000758e-08
    See output-gmg/solver_history.txt for the full convergence history.

    void dealii::SolverFGMRES<VectorType>::solve(const MatrixType&,
    VectorType&, const VectorType&, const PreconditionerType&) [with
    MatrixType = aspect::internal::StokesBlock; PreconditionerType =
    aspect::internal::BlockSchurPreconditioner<dealii::TrilinosWrappers::PreconditionAMG,
    dealii::TrilinosWrappers::PreconditionBase>; VectorType =
    dealii::TrilinosWrappers::MPI::BlockVector]
    The violated condition was:
    false
    Additional information:
    Iterative method reported convergence failure in step 2000. The
    residual in the last step was 1.90377e-08.

Originally posted by @zjiaqi2018 in https://github.com/geodynamics/aspect/pull/4852#issuecomment-1243046122

[tjhei]

Let's check if this is still an issue.

[gassmoeller]

To be clear, the starter project part here is just to run the benchmark and check if there are still issues. Fixing the issues will likely be complicated.