CMS 6 - Enforce minimum version of egulias dep

[emteknetnz]

We are getting literally thousands of deprecation notices on --prefer-lowest builds e.g. https://github.com/silverstripe/recipe-core/actions/runs/11468619556/job/31914133348

PHP Deprecated: Function utf8_encode() is deprecated in /home/runner/work/recipe-core/recipe-core/vendor/egulias/email-validator/src/EmailLexer.php on line 275

Notes

• May be resolved by Upgrade third-party composer dependencies .github#306

Acceptance criteria

• Prefer lowest builds install a version of the egulias dep that does not trigger deprecation notice, either through "require" or "conflict", whichever makes the most sense

[GuySartorelli]

I think there used to be a conflict that I probably thought "we can't possibly need that anymore" 😅 I wish we could add comments to composer.json.
We should probably add it as an explicit dependency.