docs: add JohannesFischer as a contributor for code

[allcontributors]

Add @JohannesFischer as a contributor for code.

This was requested by ph-fritsche in this comment

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[codecov]

Codecov Report

Merging #745 (f359f44) into main (f731f68) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##              main      #745   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           50        50           
  Lines          965       965           
  Branches       389       389           
=========================================
  Hits           965       965           

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[github-actions]

🎉 This PR is included in version 13.4.1 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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