Fix warnings in docs build

[jlaehne]

Description of the change

Address warnings in building of documentation

Progress of the PR

• Change implemented (can be split into several points),
• update user guide (if appropriate),
• ready for review.

[codecov-commenter]

Codecov Report

Base: 100.00% // Head: 100.00% // No change to project coverage 👍

Coverage data is based on head (4644bba) compared to base (da723d8).
Patch has no changes to coverable lines.

❗ Current head 4644bba differs from pull request most recent head 28468cd. Consider uploading reports for the commit 28468cd to get more accurate results

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #163   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           11        11           
  Lines          548       548           
=========================================
  Hits           548       548           

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