docs: stay on the same page when switching website versions

[jponge]

See https://squidfunk.github.io/mkdocs-material/setup/setting-up-versioning/#stay-on-the-same-page-when-switching-versions

Note that this won't fix older published releases.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.05%. Comparing base (36e2e92) to head (ac443b1).
Report is 25 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1836      +/-   ##
============================================
- Coverage     89.10%   89.05%   -0.05%     
  Complexity     3271     3271              
============================================
  Files           459      459              
  Lines         13388    13388              
  Branches       1659     1659              
============================================
- Hits          11929    11923       -6     
- Misses          821      825       +4     
- Partials        638      640       +2     

see 6 files with indirect coverage changes

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