pace/tests/main/grid/test_eta.py moved to NDSL/tests/grid/test_eta.py

[fmalatino]

Description This PR moves the unit test: test_eta.py out of pace/tests/main/grid into NDSL/tests/grid, as NDSL handles hybrid pressure variable initialization. Within pace, one can still run the test if needed after installation of NDSL.

This PR should be merged before PR 65 in NDSL.

How Has This Been Tested? Tested using the remaining unit tests in pace.

Checklist:

• [x] My code follows the style guidelines of this project
• [x] 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