Fix compilation against recent Slurm.

Tested against Slurm 24.11.

Note: slurm_hostlist_ranged_string_malloc was changed to slurm_hostlist_ranged_string_xmalloc and the resulting object should be freed via xfree. However I can't figure out where to get xfree from, so the calls have been commented out. This means that opa2slurm will now leak a bit of memory, but since it's just run as a one-off job, that seems a minor issue.