[TASK] Avoid PHP 8.2 deprecation messages in CSP backend module

Replace "self" in callables by their first class callable syntax.

Resolves: #100534
Related: #99499
Releases: main
Change-Id: I9cdc016d018dd8fa7fbed22c0f5bc4e67fcc1b5d
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/78544


Tested-by: Oliver Hader <oliver.hader@typo3.org>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>