Update CHECKOUT_code: FMScoupler checkout

[laurenchilutti]

Description

The current CHECKOUT_code script was not specifying a tag for FMScoupler. This repository should be checked out with the same tag that we checkout FMS with.

Fixes # (issue)

How Has This Been Tested?

Testing on GAEA

Checklist:

Please check all whether they apply or not

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] Any dependent changes have been merged and published in downstream modules

[laurenchilutti]

@JosephMouallem When your changes to FMScoupler for SHiELD MOM6 and FMS Coupler are merged in and tagged, we can also update this checkout script to use that newer tag