Fixed chessboard references

[Shivansh20128]

Description

This PR fixes the references for the states/chessboard.py as discussed in the mentioned issue.
#Closes #843

Changes

• Added "Bruß_2000_Construction" reference in refs.bib
• Modified reference in chessboard.py

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.9%. Comparing base (c5d23d6) to head (ff27f70).
Report is 2 commits behind head on master.

Additional details and impacted files

@@          Coverage Diff           @@
##           master    #895   +/-   ##
======================================
  Coverage    97.9%   97.9%           
======================================
  Files         168     168           
  Lines        3293    3293           
  Branches      721     721           
======================================
  Hits         3225    3225           
  Misses         44      44           
  Partials       24      24           

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[vprusso]

That's great work, @Shivansh20128 !

LGTM, and thank you again!