test(cli): Create cli/spinner `Spinner` tests using Deno.Command.spawn()

[JakeAve]

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Adding tests for @std/cli/spinner per #4672 . Open to feedback.

[codecov[bot]]

Codecov Report

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

Project coverage is 91.44%. Comparing base (ea70808) to head (6192aa1). Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4713      +/-   ##
==========================================
- Coverage   91.47%   91.44%   -0.03%     
==========================================
  Files         477      480       +3     
  Lines       37240    37324      +84     
  Branches     5311     5320       +9     
==========================================
+ Hits        34065    34132      +67     
- Misses       3119     3136      +17     
  Partials       56       56              

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[iuioiua]

One of these tests appears to be flaky: https://github.com/denoland/deno_std/actions/runs/9058079848/job/24883108851