fix: qty_potential_temperature 3d interpolate in wrf model_mod

[hkershaw-brown]

Description:

fix: qty_potential_temperature 3d interpolate in wrf model_mod
k+1 level was using k value for x_iul value

Fixes issue

fixes #1011

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 not work as expected)
• Documentation update

Documentation changes needed?

• My change requires a change to the documentation.
  • I have updated the documentation accordingly.

Tests

Please describe any tests you ran to verify your changes.

Compared against wrf_unified branch using a function for interpolation for levels k& k+1

DART/models/wrf_unified/model_mod.f90

Line 839 in 41563dd

function simple_interpolation(ens_size, state_handle, qty, id, ll, ul, lr, ur, k, dxm, dx, dy, dym)

Not tested assimilation, this change will be answer changing.

Checklist for merging

• Updated changelog entry
• Documentation updated
• Update conf.py

Checklist for release

• Merge into main
• Create release from the main branch with appropriate tag
• Delete feature-branch

Testing Datasets

• Dataset needed for testing available upon request
• Dataset download instructions included
• No dataset needed