fix: set include_cross_pols to False if feed_array has length 1

[steven-murray]

Description

This simply fixes behavior when setting only a single feed in an AnalyticBeam. You can manually get around this on initialization by setting include_cross_pols=False, but you can't do this when updating an existing object, i.e.

from pyuvdata.analytic_beam import GaussianBeam
from dataclasses import replace

beam = GaussianBeam(diameter=14.0)
new_beam = replace(beam, feed_array=['x'])

This would fail due to the issue resolved here, and you can't specify include_cross_pols in the replace() call, because it's an init-only parameter.

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 99.93%. Comparing base (4e6f3ed) to head (d32869a).
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1495   +/-   ##
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  Coverage   99.93%   99.93%           
=======================================
  Files          63       63           
  Lines       21748    21750    +2     
=======================================
+ Hits        21733    21735    +2     
  Misses         15       15           

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[bhazelton]

Looks good.