ALUGrid tests fail with libc++

When running an updated toolchain with clang and libc++ the parallel ALUGrid tests fail, see, e.g., https://gitlab.dune-project.org/infrastructure/dune-nightly-test/-/jobs/615638

When running the code locally, I get a segfault during the traversal of the periodic map. It might be that the iteration + erase pattern is not implemented correctly. Follwing the stackoverflow answer https://stackoverflow.com/a/8234813 seems to eliminate the segfault and the tests pass locally.