[DOCS] Fix missing quotation marks in PHP code examples

Resolves: #97321
Releases: main
Change-Id: Ifbbd0e4961ed2c17beebadb0d2eb732fdd05f6a0
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/74202


Tested-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>