Correctly pass spline_opts to new uvbeam interpolator

[tyler-a-cox]

This PR fixes a small bug introduced by a previous PR, where a new interpolation method was added to pyuvdata. In the previous PR, I did not correctly pass the spline_opts parameter to _interp_az_za_map_coordinates.

Description

This PR modifies an if statement to correctly pass the interpolation keyword arguments.

Motivation and Context

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 change)
• Documentation change (documentation changes only)
• Version change
• Build or continuous integration change

Checklist:

• I have read the contribution guide.
• My code follows the code style of this project.

Bug fix checklist:

• My fix includes a new test that breaks as a result of the bug (if possible).
• All new and existing tests pass.
• I have updated the CHANGELOG.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.92%. Comparing base (e5309ef) to head (2ae6128).
Report is 155 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1474   +/-   ##
=======================================
  Coverage   99.92%   99.92%           
=======================================
  Files          61       61           
  Lines       21337    21337           
=======================================
  Hits        21322    21322           
  Misses         15       15           

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[steven-murray]

LGTM