Replace Mumps by SuperLU_dist in test models

Currently recent PETSc (3.16+) uses up an updated version of Mumps... which fails frequently (but not always...) in parallel runs.

The issue has been reported and is still discussed with both PETSc and Mumps dev, but for the time being I'm not very optimistic for its quick resolution.

(the error appeared in PETSc commit c8f33523d98b21992ab424d9d203d22698ee7011, which changes the version of Mumps used in macOS - prior to this commit an older Mumps was used for macOS. The way the change is done can't be easily reverted locally).

As a result, the test about models will be ported in SuperLU_dist (another embedded solver in PETSc which works properly and was introduced in #1704).

A warning message will be added in MoReFEM when use of Mumps is attempted on macOS.