docs(userMutationObserverRef): fix examples and code sandboxes

[qiweiii]

Closes: #529

[codecov]

Codecov Report

Merging #556 (7049756) into main (e5a55ec) will increase coverage by 1.07%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #556      +/-   ##
==========================================
+ Coverage   71.85%   72.93%   +1.07%     
==========================================
  Files          65       66       +1     
  Lines        1304     1319      +15     
  Branches      262      265       +3     
==========================================
+ Hits          937      962      +25     
+ Misses        366      356      -10     
  Partials        1        1              

Impacted Files	Coverage Δ
src/hooks/useDebouncedValue.ts	93.33% <0.00%> (ø)
src/hooks/useDebounce.ts	93.33% <0.00%> (+73.33%)	⬆️

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[github-actions]

🎉 This PR is included in version 5.6.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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