Fortran: Accept again tab as alternative to space as separator [PR114304]

This fixes a side-effect of/regression caused by r14-9822-g93adf88cc6744a,
which was for the same PR.

	PR libfortran/114304

libgfortran/ChangeLog:

	* io/list_read.c (eat_separator): Accept tab as alternative to space.

gcc/testsuite/ChangeLog:

	* gfortran.dg/pr114304-2.f90: New test.