[BUGFIX] Add missing label to modal close button

We also ensure that TYPO3.lang checks are correct
when the modal is used in a context where TYPO3.lang
is not defined.

Resolves: #101844
Releases: main, 12.4, 11.5
Change-Id: I1e6e90ed86e72f483929429b8e2c833179b60f87
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/80867


Tested-by: Benjamin Franzke <ben@bnf.dev>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Benjamin Franzke <ben@bnf.dev>