[BUGFIX] Loosen types for PSR-7 message implementation

This change allows user-lang code when using
TYPO3's PSR-7 implementation to also use integers
and floats for header values.

This change popped up in PHP 8.0 environments.

Resolves: #101001
Releases: main, 12.4, 11.5
Change-Id: Ia4d3309ef5c6c4f4357eed75bb0ddad40503d132
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/79780


Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>