Fix PHPStan level 0 issues in themes #25641

Job	Run time
Core running from build / MacOS	11m 7s
Core running from src / MacOS	14m 15s
Core running from src / Linux	6m 45s
Core running from build / Linux	8m 13s
Core running from src / Windows	11m 17s
Core running from build / Windows	11m 16s
Slack Notifications	0s
Failed workflow tasks	0s
	1h 2m 53s

Provide feedback