Fix aria label of item-navigator icons literal instead of functional

[cdrini]

Sister PR: https://github.com/internetarchive/iaux-item-navigator/pull/23 . See the docs + video there. This is unfortunately difficult to demo otherwise.

[codecov[bot]]

Codecov Report

:x: Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review. :white_check_mark: Project coverage is 69.43%. Comparing base (970f0c9) to head (1e437b2). :warning: Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
src/BookNavigator/bookmarks/bookmarks-provider.js	0.00%	1 Missing :warning:

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1464   +/-   ##
=======================================
  Coverage   69.43%   69.43%           
=======================================
  Files          62       62           
  Lines        5329     5329           
  Branches     1155     1155           
=======================================
  Hits         3700     3700           
  Misses       1594     1594           
  Partials       35       35           

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[cdrini]

Auto-merging ; smaller change, most changes in https://github.com/internetarchive/iaux-item-navigator/pull/23