Docs: Update part-6-performance-normalization.md

[yoles]

Fixed typo in router

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name: :memo: Documentation Fix about: Fixing a problem in an existing docs page

Checklist

• [X] Is there an existing issue for this PR? No
• [X] Have the files been linted and formatted? Yes

What docs page needs to be fixed?

• Section: #adding-user-pages
• Page: https://redux.js.org/tutorials/essentials/part-6-performance-normalization

What is the problem?

React router dom, strictly use element attribute since v6 instead of component

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[timdorr]

Thanks!