Increase length of char variables "parent1" and "parent2" in
set_syms_host_assoc() to allow them to hold concatenated module +
submodule names.

        PR fortran/93473
        * parse.c: Increase length of char variables to allow them to hold
        a concatenated module + submodule name.
        * gfortran.dg/pr93473.f90: New test.