build(deps): bump mkdocs-material to 9.0.0

[mkniewallner]

PR Checklist

• A description of the changes is added to the description of this PR.
• If there is a related issue, make sure it is linked to this PR.
• If you've fixed a bug or added code that should be tested, add tests!
• Documentation in docs is updated

Description of changes

Changelog: https://github.com/squidfunk/mkdocs-material/releases/tag/9.0.0
Upgrade guide: https://squidfunk.github.io/mkdocs-material/upgrade/#upgrading-from-8x-to-9x

Also removing mkdocstrings since it's not currently used.

[codecov-commenter]

Codecov Report

Merging #258 (8579346) into main (6897cc4) will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##            main    #258   +/-   ##
=====================================
  Coverage   95.7%   95.7%           
=====================================
  Files         32      32           
  Lines        922     922           
  Branches     193     193           
=====================================
  Hits         883     883           
  Misses        26      26           
  Partials      13      13           

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