[FOLLOWUP][BUGFIX] Allow longer file-endings in typoscript directory includes

[FOLLOWUP][BUGFIX] Allow longer file-endings in typoscript directory includes

Adds missing unit tests for this change.

Resolves: #82543
Releases: master, 8.7
Change-Id: Ica7f5c2f99dd991042e3c1166f7806534bf24421
Reviewed-on: https://review.typo3.org/54460
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Joerg Boesche <typo3@joergboesche.de>
Tested-by: Joerg Boesche <typo3@joergboesche.de>
Reviewed-by: Henning Liebe <h.liebe@neusta.de>
Tested-by: Henning Liebe <h.liebe@neusta.de>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>