test: cover dynamically updated closeOnEsc prop

[pradel]

Closes #504.

The bug (a stale closeOnEsc closure captured by the document keydown listener) shared its root cause with #524 and was fixed in #573: the listener is now registered in an effect that depends on closeOnEsc, so it always uses the latest prop value.

This PR adds regression tests that lock the behavior in:

• closeOnEsc updated from true to false while the modal is open does not close on esc.
• closeOnEsc updated from false to true while the modal is open closes on esc.

Both pass on master and fail when the #573 source fix is reverted.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.69%. Comparing base (78a46ea) to head (4645957).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #576   +/-   ##
=======================================
  Coverage   80.69%   80.69%           
=======================================
  Files           7        7           
  Lines         202      202           
  Branches       74       74           
=======================================
  Hits          163      163           
  Misses         29       29           
  Partials       10       10           

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