[TASK] Add unit tests for mailto_makelinks

Increase code coverage with some more tests.

Resolves: #97444
Related: #97303
Releases: main, 11.5
Change-Id: Icaa20aea45bc34b5618bfc55710014d928444510
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/74466


Tested-by: Simon Schaufelberger <simonschaufi+typo3@gmail.com>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Simon Schaufelberger <simonschaufi+typo3@gmail.com>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>