How to upgrade to Drupals latest version via Composer?
I had exactly the same issue while performing upgrades. The solution for me was removing/renaming the vendor folder and the composer.lock file and run composer update drupal/core --with-dependencies.

You can also try to update dependency explicitly with composer update egulias/email-validator drupal/core --with-dependencies. This usually works in this type of issues, but it didn't work for me.

Given that you don't see drupal/core in your composer.json you might also try composer require drupal/core.