fix: skip repeated key events when the slash menu is opening

[LucasXu0]

Skip repeated key events when the slash menu is opening

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 17 lines in your changes missing coverage. Please review.

Project coverage is 72.19%. Comparing base (817c965) to head (9c28c73).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...c/editor/selection_menu/selection_menu_widget.dart	0.00%	17 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #978      +/-   ##
==========================================
- Coverage   72.25%   72.19%   -0.06%     
==========================================
  Files         318      318              
  Lines       15132    15144      +12     
==========================================
  Hits        10933    10933              
- Misses       4199     4211      +12     

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