[BUGFIX] Use proper type for recovery emails

RecoveryService::prepareMail creates a FluidEmail, but
returns it as Symfony\Component\Mime\Email. Setting the
signature to the proper type, which also is used in the
SendRecoveryEmailEvent, allows easier adjustment of the
sent email.

Resolves: #100174
Releases: main, 12.4
Change-Id: Ic88e23fea52cfc6f61efc885eb24267fb461628f
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/78384


Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Tested-by: Torben Hansen <derhansen@gmail.com>
Reviewed-by: Torben Hansen <derhansen@gmail.com>
Tested-by: Oliver Hader <oliver.hader@typo3.org>