Fix entropy_mutual when the input state is Ket

[ytdHuang]

Checklist

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• Please read Contributing to Quantum Toolbox in Julia.
• Any code changes were done in a way that does not break public API.
• Appropriate tests were added and tested locally by running: make test.
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Description

As title.

This also fix the build error in the tutorial.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.18%. Comparing base (3d013a7) to head (74992db).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #716      +/-   ##
==========================================
- Coverage   93.22%   93.18%   -0.05%     
==========================================
  Files          57       57              
  Lines        3914     3915       +1     
==========================================
- Hits         3649     3648       -1     
- Misses        265      267       +2     

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