Fix broken links to the human-in-the-loop optimization tutorial

[c-bata]

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This pull request may therefore be ported to Goptuna.
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Reference Issues/PRs

Fixes #667

What does this implement/fix? Explain your changes.

Fix broken links to the human-in-the-loop optimization tutorial

[codecov]

Codecov Report

Merging #671 (29a5833) into main (14afdee) will increase coverage by 0.23%.
Report is 11 commits behind head on main.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##             main     #671      +/-   ##
==========================================
+ Coverage   62.65%   62.88%   +0.23%     
==========================================
  Files          35       35              
  Lines        2252     2250       -2     
==========================================
+ Hits         1411     1415       +4     
+ Misses        841      835       -6     

Files	Coverage Δ
optuna_dashboard/preferential/samplers/gp.py	70.35% <66.66%> (+2.37%)	⬆️

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