fix: don't allow email aliases on registration

[ciurana-life]

Description

• Issue reported at https://github.com/zenodo/ops/issues/537#event-30039858466

• Related to fix: Prevent html injection in ProfileForm invenio-userprofiles#202

• It was possible to re-send the account creation email to a registered user using an alias

• Combined with injecting a url on the email this was a problem

• No impact on account creation since no email provider allows normal accounts to contain "+" when creating them

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