Small test fix for an update to pyuvdata's handling for rdate in uvfits

[bhazelton]

Description

This is a small fix for a test that started erroring as a result of a fix in pyuvdata's handling of the UVFITS parameter rdate.

This is inconsequential as far as pyuvsim functionality goes.

Motivation and Context

Types of changes

• [x] 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)
• [ ] Reference simulation update or replacement
• [ ] Documentation change (documentation changes only)
• [ ] Version change
• [ ] Build or continuous integration change

Checklist:

For all pull requests:

• [x] I have read the contribution guide.
• [x] 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).
• [x] All new and existing tests pass.
• [ ] I have checked that I reproduce the reference simulations or if there are differences they are explained below (if appropriate). If there are changes that are correct, I will update the reference simulation files after this PR is merged.
• [ ] I have checked (e.g., using the benchmarking tools) that this change does not significantly increase typical runtimes. If it does, I have included a justification in the comments on this PR.
• [ ] I have updated the CHANGELOG.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 100.00%. Comparing base (c4994d1) to head (b5315fe).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #471 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 11 11 Lines 2165 2165 ========================================= Hits 2165 2165 ```

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