[Fix for the GitLab CI] phist: prefer @1.9.5 (1.9.6 is not compatible w/ mpich%gcc:9) (#26773)
[Fix for the GitLab CI] phist: prefer @1.9.5 (1.9.6 is not compatible w/ mpich%gcc:9) (#26773)

* phist: Prefer 1.9.5 (1.9.6 uses mpi_f08, but not available in CI)

* phist: remove dupe of 1.9.5, missing preferred=True

Also, for 1.9.6, patch the (most, one does not work) tests to use
LLNL/spack,LLNL/spack,LLNL/spack,LLNL/spack,LLNL/spack