Fix so that write_uvfits doesn't change the object, add loopback testing

[bhazelton]

Description

This fixes a minor problem with the recent addition of the use_miriad_convention keyword to uvfits.

Namely, it could actually change the antenna numbers on the object, which wasn't desirable (and it didn't update the baseline_array to match).

This also adds some loopback testing to ensure that pyuvdata can properly read in a file written out with use_miriad_convention=True.

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 ✅

Comparison is base (4d66558) 99.92% compared to head (e1ab6f0) 99.92%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1393   +/-   ##
=======================================
  Coverage   99.92%   99.92%           
=======================================
  Files          37       37           
  Lines       20445    20446    +1     
=======================================
+ Hits        20429    20430    +1     
  Misses         16       16           

Files	Coverage Δ
pyuvdata/uvdata/uvfits.py	100.00% <100.00%> (ø)

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[kartographer]

Looks good, thanks @bhazelton!