Need to update git-fleximod version

### Issue Type

Externals Update

### Issue Description

With the addition of PUMAS and RRTMGP physics there will be submodules within submodules, as the atmospheric_physics submodule will be calling the ccpp-physics submodule that itself is calling the PUMAS and RRTMGP submodules. This sometimes doesn't work with the older version of git-fleximod currently used in CAM-SIMA, so the git-fleximod version should be updated so that the nested git submodule checkout works as expected.

### Will this change answers?

No

### Will you be implementing this yourself?

Any Software Engineer can do this