test: tests for slices with Vec as subject should take a reference to the Vec

[haraldmaida]

Some tests for slices use a Vec as subject and give the owned Vec to the assert_that() function. These tests are actually duplicates to tests in the vec module.

Instead the tests in the slice module should call the assert_that() function giving a reference to the Vec.

Those tests have been fixed to take a reference to the Vec.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.95%. Comparing base (399c809) to head (2230882).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #69   +/-   ##
=======================================
  Coverage   93.95%   93.95%           
=======================================
  Files          32       32           
  Lines        4463     4463           
  Branches     4463     4463           
=======================================
  Hits         4193     4193           
  Misses        233      233           
  Partials       37       37           

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