docs: fix typo in uploader document

[Uyoahz26]

This pull request includes a minor correction to the documentation for the before-delete hook in the Uploader component. The change clarifies that returning false stops the deletion of the file, rather than stopping the reading of the file.

Documentation updates:

• packages/vant/src/uploader/README.md: Corrected the description for the before-delete hook to specify that returning false stops file deletion.
• packages/vant/src/uploader/README.zh-CN.md: Updated the Chinese documentation for the before-delete hook to clarify that returning false stops file deletion.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.74%. Comparing base (ec5b45b) to head (3c2e4e6).
Report is 101 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #13502      +/-   ##
==========================================
+ Coverage   89.60%   89.74%   +0.14%     
==========================================
  Files         257      257              
  Lines        7013     7033      +20     
  Branches     1736     1741       +5     
==========================================
+ Hits         6284     6312      +28     
+ Misses        384      379       -5     
+ Partials      345      342       -3     

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[chenjiahan]

thank you