Fix sass deprecation in Bootstrap

[camd]

Relies on #9112 which must be merged first.

This was minor, but still showed up as a deprecation.

[codecov-commenter]

Codecov Report

:x: Patch coverage is 44.44444% with 5 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 79.95%. Comparing base (5d64caf) to head (4daf59e).

Files with missing lines	Patch %	Lines
ui/App.jsx	44.44%	5 Missing :warning:

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #9113   +/-   ##
=======================================
  Coverage   79.95%   79.95%           
=======================================
  Files         600      600           
  Lines       32560    32560           
  Branches     3310     3310           
=======================================
  Hits        26032    26032           
  Misses       6362     6362           
  Partials      166      166           

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[camd]

Abandoning in favor or RSPack approach.