docs: Update dependencies and workaround further style issues

[stotko]

Recently, several of our dependencies for the documentation received some updates. While there seem to be some issues with the styling, it is still better to keep them up to date. Remove the restriction on the Sphinx Book Theme and add some workaround for the style issues.

The doxygen version is kept fixed for the time being as this requires some further testing as well as checking if e.g. doxysphinx is compatible.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.33%. Comparing base (965a29f) to head (7ec95e1).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #419      +/-   ##
==========================================
- Coverage   97.37%   97.33%   -0.04%     
==========================================
  Files          31       31              
  Lines        2512     2512              
==========================================
- Hits         2446     2445       -1     
- Misses         66       67       +1     

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