[BUGFIX] Only set Content-Type charset if no charset is given

When using TYPO3 as a response for multipart
result or application/binary responses,
TSFE should not append "charset=utf-8" to the
Content-Type HTTP response header.

Resolves: #100189
Related: #99373
Related: #97550
Releases: main, 11.5
Change-Id: I645bb6941bb4bd01cb508a873e1add074c39ca57
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/78171


Tested-by: Benni Mack <benni@typo3.org>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Achim Fritz <af@achimfritz.de>
Reviewed-by: Achim Fritz <af@achimfritz.de>