Fix issue #7532: Disabled for NestedSelect

[mayonnaisecolouredbenz7]

Description

This pull request fixes issue #7532 .

Changes Made

• Fixed the disabled toggle for NestedSelect
• Not sure if this is it what is required. But is working as expected
• Documentation doesn't show disabled as a parameter, however the original code did have references to it so looks like it is intended and is inline with other widgets
• Ran tests locally with pixi before opening this PR

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.21%. Comparing base (4e4c82b) to head (cd675d7).
Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7533      +/-   ##
==========================================
- Coverage   82.22%   82.21%   -0.02%     
==========================================
  Files         339      339              
  Lines       51321    51322       +1     
==========================================
- Hits        42198    42193       -5     
- Misses       9123     9129       +6     

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[ahuang11]

Thanks for adding this! Can you add it to the reference notebook https://github.com/holoviz/panel/blob/main/examples/reference/widgets/NestedSelect.ipynb and maybe add a test too https://github.com/holoviz/panel/blob/main/panel/tests/widgets/test_select.py#L260 by checking the sub-widgets are disabled too.

Also, maybe you sync loading too.