`NonoverlappingRichardson` doesn't correctly implement the `Dune::Preconditioner` interface

This method and this method are marked const but the respective methods in the base class in ISTL are not, so using the NonoverlappingRichardson preconditioner does not compile.

I don't think that the signature of Preconditioner::{pre, apply} was recently changed in ISTL, so I think this is just a typo. I can open a MR with a fix and also add a test case (or rather test cases, it seems that most (all?) solvers in novlpistlsolverbackend.hh aren't tested anywhere).

Yes, it seems to be just a typo. A MR would be nice!

BTW, when providing links to code, try to link permalinks so that they are still point to the same line after the modifications are made. This way is easier to back track past issues/changes.

changed milestone to %PDELab 2.10

mentioned in merge request !643 (merged)

closed with merge request !643 (merged)

mentioned in commit 2c31b3bc