[TASK] Test cases for function specCharsToASCII()

Add a new test for the function specCharsToASCII().

Resolves: #83546
Related: #20612
Releases: master
Change-Id: Id255ab953ef7c1865a7db1892b9b5d5fac87c547
Reviewed-on: https://review.typo3.org/55333


Reviewed-by: Reiner Teubner <rteubner@me.com>
Tested-by: Reiner Teubner <rteubner@me.com>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>