GEFSv12: Update UPP tag to gefs_v12.3.20

[EricSinsky-NOAA]

Description

This PR updates the UPP tag for GEFSv12 to gefs_v12.3.20.

Addresses #4885

Type of change

• Bug fix (fixes something broken)
• New feature (adds functionality)
• Maintenance (code refactor, clean-up, new CI test, etc.)

Change characteristics

• Is this change expected to change outputs (e.g. value changes to existing outputs, new files stored in COM, files removed from COM, filename changes, additions/subtractions to archives)? YES/NO (If YES, please indicate to which system(s))
  • GFS
  • GEFS
  • SFS
  • GCAFS
• Is this a breaking change (a change in existing functionality)? YES/NO
• Does this change require a documentation update? YES/NO
• Does this change require an update to any of the following submodules? YES/NO (If YES, please add a link to any PRs that are pending.)
  • EMC verif-global
  • GDAS
  • GFS-utils
  • GSI
  • GSI-monitor
  • GSI-utils
  • UFS-utils
  • UFS-weather-model
  • wxflow

How has this been tested?

checkout.sh has been tested and the proper upp tag is checked out.

Checklist

• Any dependent changes have been merged and published
• 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 documented my code, including function, input, and output descriptions
• My changes generate no new warnings
• New and existing tests pass with my changes
• This change is covered by an existing CI test or a new one has been added
• Any new scripts have been added to the .github/CODEOWNERS file with owners
• I have made corresponding changes to the system documentation if necessary

[EricSinsky-NOAA]

A release tag has been created for gefs_v12.3.20-0.