[BUGFIX] Use proper methods of symfony/mime

Fix missing parts after the migration from swiftmailer to symfony/mime

Resolves: #88849
Releases: master
Change-Id: I3d30589cac44ff7d387a49857bb1f7820c580138
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/61383


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Susanne Moog <look@susi.dev>
Tested-by: Josef Glatz <josefglatz@gmail.com>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Jörg Bösche <typo3@joergboesche.de>
Reviewed-by: Susanne Moog <look@susi.dev>
Reviewed-by: Josef Glatz <josefglatz@gmail.com>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>