Rename test files that contain jsx syntax to have a jsx file suffix

[jcoyne]

This supports a Vite 8 upgrade.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.9%. Comparing base (eddb128) to head (2f28688).

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #4288     +/-   ##
=======================================
- Coverage   93.0%   92.9%   -0.1%     
=======================================
  Files        335     335             
  Lines       5538    5538             
  Branches    1955    1955             
=======================================
- Hits        5149    5143      -6     
- Misses       346     348      +2     
- Partials      43      47      +4     

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[marlo-longley]

@jcoyne not sure if you are aware but I made a number of commits to your other vite 8 PR, including this change

#4260

[jcoyne]

@marlo-longley yes, but I think it makes sense to make this change in it's own PR as it doesn't depend on any specific vite version. It's good practice to have the file extension match the file type.