bug: mom6 find_bounds_levels for pseudo depth giving incorrect fraction.

[hkershaw-brown]

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Describe the bug

1. List the steps someone needs to take to reproduce the bug.
   Run model_mod_check with use_pseudo depth = .true.
   u current netcdf variable modified to be 1,2,3,4,5, for each layer
2. What was the expected outcome?
   Correct vertical interpolation
3. What actually happened?
   looking at the lev_frac, wrong fraction (-ve) for vertical interpolation

Error Message

No error messages, print outs from model_mod_check:

interpolating at  Lon/Lat(deg): 179.00000000  11.00000000  Vert:    4.5000000 km
interpolating for "QTY_U_CURRENT_COMPONENT"
-------------------------------------------------------------

 i          73
 vert_loc   4500.0000000000000       zstar(lev(1))   4803.0000000000000       zstar(lev(2))   4436.8999999999996     
 expected at level below obs   73.000000000000000      expected at level above obs   72.000000000000000       lev_fract -0.82764272056814991     
member     1, SUCCESS with value    ::    73.827642720568150

Which model(s) are you working with?

MOM6

Version of DART

Which version of DART are you using?
You can find the version using git describe --tags
v11.20.1-1-g76de4fc27

Have you modified the DART code?

Yes, printing out the various level values, & fraction.

Build information

Please describe:

1. mac GNU Fortran (MacPorts gcc13 13.3.0_2+stdlib_flag) 13.3.0
2. The compiler you are using (e.g. gnu, intel).