small fix

[bitterbark]

The catalog parser wouldn't run for me without this small change.

How Has This Been Tested?
Run on CESM data, NCAR's casper machine

Checklist:

• [x ] My branch is up-to-date with the NOAA-GFDL main branch, and all merge conflicts are resolved
• [x ] The scripts are written in Python 3.12 or above (preferred; required if funded by a CPO grant), NCL, or R
• [ n/a] All of my scripts are in the diagnostics/[POD short name] subdirectory, and include a main_driver script, template html, and settings.jsonc file
• [ n/a] I have made corresponding changes to the documentation in the POD's doc/ subdirectory
• [ n/a] I have requested that the framework developers add packages required by my POD to the python3, NCL, or R environment yaml file if necessary, and my environment builds with conda_env_setup.sh
• [n/a ] I have added any necessary data to input_data/obs_data/[pod short name] and/or input_data/model/[pod short name]
• [ n/a] My code is portable; it uses MDTF environment variables, and does not contain hard-coded file or directory paths
• [ n/a] I have provided the code to generate digested data files from raw data files
• [n/a ] Each digested data file generated by the script contains numerical data (no figures), and is 3 GB or less in size
• [ n/a] I have included copies of the figures generated by the POD in the pull request
• [ n/a] The repository contains no extra test scripts or data files