[TEST] Change test s.t. sort by cardinality is stable.

[smehringer]

Todo:

• Change other many_ubs tests

Note: There is one test, that cannot really be made "stable by only unique sizes" because it uses actual files as input, but these files repeatedly. The file size cannot be changed.
This, for now, automatically tests, what happens with non-unique user bin sizes.

[seqan-actions]

Documentation preview available at https://docs.seqan.de/preview/seqan/chopper/257

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.72%. Comparing base (c3fe1f9) to head (27d7ad4).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #257   +/-   ##
=======================================
  Coverage   95.72%   95.72%           
=======================================
  Files          20       20           
  Lines         749      749           
  Branches       15       15           
=======================================
  Hits          717      717           
  Misses         32       32           

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