docs: fix docs site redirect rule

[krancour]

This is a "forward port." The release-1.0 branch, which is the production docs branch, already has this fix.

I want it in main now so we don't lose the fix when we create a release-1.1 branch in a few weeks.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 48.79%. Comparing base (f2ee9a8) to head (232c73d).
Report is 5 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2814   +/-   ##
=======================================
  Coverage   48.79%   48.79%           
=======================================
  Files         270      270           
  Lines       23962    23962           
=======================================
  Hits        11692    11692           
  Misses      11639    11639           
  Partials      631      631           

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