[BUGFIX] Fix PHP 8.1 warnings in ExtbasePluginEnhancer

Resolves: #98059
Releases: main, 11.5
Change-Id: I078db9039c2f0acb05933fa6a86ca5d73b3fb5d7
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/75337


Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>