fix: Paste option shows when it shouldn't

[ericlln]

Useful snippet for testing

from deephaven import empty_table, input_table
source = empty_table(10).update(["X = i", "Y = i"])
result = input_table(init_table=source)

• The source table is not an input table and now has no option to paste into any cells
• The result table is an input table, and the option to paste will appear only if the current selection can be pasted into

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 21 lines in your changes missing coverage. Please review.

Project coverage is 46.74%. Comparing base (9d49873) to head (f471069).

Files with missing lines	Patch %	Lines
...d/src/mousehandlers/IrisGridContextMenuHandler.tsx	0.00%	21 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2364      +/-   ##
==========================================
- Coverage   46.75%   46.74%   -0.02%     
==========================================
  Files         710      710              
  Lines       39116    39125       +9     
  Branches     9775     9964     +189     
==========================================
  Hits        18289    18289              
- Misses      20816    20825       +9     
  Partials       11       11              

Flag	Coverage Δ
unit	46.74% <0.00%> (-0.02%)	⬇️

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