dmUpdate: Fix so that filenames are not saved in lowercase

[uramirez8707]

Description
Removes the lowercase when saving the filenames into the sorted list of files. This sorted list is used to find the file_ids of the variables when the variable is registered using a binary search (for performance). The filename should be saved as it is saved in the yaml object.

Without this change, we are getting errors such as
/gpfs/f5/gfdl_f/scratch/Niki.Zadeh/FMS2024.01-beta1_mom6_20231130_ymal_1/OM4p5_CORE2_IAF_COBALT4.0_abio_csf_mle200/ncrc5.intel23-pr
od/stdout/run/OM4p5_CORE2_IAF_COBALT4.0_abio_csf_mle200_1x1m0d_1057x1o1.o134750073

It is still needed for the variables: #1176 (comment)

Fixes # (issue)

How Has This Been Tested?
CI

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules
• New check tests, if applicable, are included
• make distcheck passes