Fix typo

Removing a typo (because I don't know how to use the GitHub editor).

src/diagnostics/MOM_sum_output.F90

@@ -4,7 +4,7 @@ module MOM_sum_output
 ! This file is part of MOM6. See LICENSE.md for the license.
 
 use iso_fortran_env, only : int64
-use MOM_checksums,     only : is_NaNis_root_pe
+use MOM_checksums,     only : is_NaN
 use MOM_coms,          only : sum_across_PEs, PE_here, root_PE, num_PEs, max_across_PEs, field_chksum
 use MOM_coms,          only : reproducing_sum, reproducing_sum_EFP, EFP_to_real, real_to_EFP
 use MOM_coms,          only : EFP_type, operator(+), operator(-), assignment(=), EFP_sum_across_PEs