Add border-radius changes to v3 migration guide

[robinmetral]

Purpose

We were missing information about the border-radius scale changes in the migration guide for v3 (implementation PR: #980)

Approach and changes

Add an entry to the migration guide with the changes and a reference to the codemod:

Definition of done

• Development completed
• Reviewers assigned
• Unit and integration tests
• Meets minimum browser support
• Meets accessibility requirements

[sumup-clark]

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[changeset-bot]

⚠️ No Changeset found

Latest commit: e523305

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[codecov]

Codecov Report

Merging #1261 (e523305) into main (a3c0412) will not change coverage.
The diff coverage is n/a.

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  Coverage   92.03%   92.03%           
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  Files         184      184           
  Lines        3630     3630           
  Branches     1170     1170           
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  Hits         3341     3341           
  Misses        271      271           
  Partials       18       18           

[connor-baer]

Looks like the Storybook docs are also outdated, @giedoka fixed this in #1260

[robinmetral]

Looks like the Storybook docs are also outdated, @giedoka fixed this in #1260

Yes we talked about that together 🙂 just updating this as well because a few teams mentioned it was missing from the migration guide