Add note about email-validator in migration guide

[Viicos]

Change Summary

Fixes #8196. Having #6033 would be nice as well.

Related issue number

Checklist

• The pull request title is a good summary of the changes - it will be used in the changelog
• Unit tests for the changes exist
• Tests pass on CI
• Documentation reflects the changes where applicable
• My PR is ready to review, please add a comment including the phrase "please review" to assign reviewers

[codspeed-hq]

CodSpeed Performance Report

Merging #8200 will not alter performance

_{Comparing Viicos:patch-2 (d5792b5) with main (64ce5b9)}

Summary

✅ 10 untouched benchmarks

[sydney-runkle]

LGTM, thanks @Viicos