The fix is obvious (I have added a comment). The tests are probably
an overkill, but it does not hurt.
libgfortran/ChangeLog:
PR fortran/93592
* io/write_float.def (build_float_string): Do not reset
nbefore for FMT_F and FMT_EN.
gcc/testsuite/ChangeLog:
PR fortran/93592
* gfortran.dg/fmt_en.f90: Adjust test.
* gfortran.dg/fmt_en_rd.f90: New test.
* gfortran.dg/fmt_en_rn.f90: New test.
* gfortran.dg/fmt_en_ru.f90: New test.
* gfortran.dg/fmt_en_rz.f90: New test.