[stable6] fix(filepicker): use proper folder icons

[backportbot]

Backport of #2180

Warning, This backport's changes differ from the original and might be incomplete ⚠️

Todo

• Review and resolve any conflicts
• Amend HEAD commit to remove the line stating to skip CI

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Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 41.78%. Comparing base (6bb6f6a) to head (b40c0b0).
⚠️ Report is 8 commits behind head on stable6.

Files with missing lines	Patch %	Lines
lib/utils/guestNameValidity.ts	0.00%	9 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           stable6    #2181   +/-   ##
========================================
  Coverage    41.78%   41.78%           
========================================
  Files           16       16           
  Lines          414      414           
  Branches        80       79    -1     
========================================
  Hits           173      173           
  Misses         214      214           
  Partials        27       27           

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