[BUGFIX] Add recipient to FluidEmail Test cases to avoid errors

The to header is mandatory by now, so we need to supply the recipient
in our testcases now.

Resolves: #91346
Releases: master
Change-Id: Ic1a3197a8412b27eb5cebb00a1443f10021b9326
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/64438


Reviewed-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>