Fixes #1912. Fixes for ACG Cmake code

[mathomp4]

Description

This PR fixes #1912 where the new ACG use in DataSea (and Ocean) were exposing a bug in the mapl_acg.cmake function. We were making assumptions on the state specs filename that were incorrect.

Related Issue

closes #1912

Motivation and Context

We should be able to do make install with no changes and get nothing recompiled!

How Has This Been Tested?

Built and tested with GEOS. Zero-diff.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Trivial change (affects only documentation or cleanup)

Checklist:

• I have tested this change with a run of GEOSgcm (if non-trivial)
• I have added one of the required labels (0 diff, 0 diff trivial, 0 diff structural, non 0-diff)
• I have updated the CHANGELOG.md accordingly following the style of Keep a Changelog