Avoid PHP 8.4 deprecations

[brotkrueml]

Summary

This PR can be summarized in the following changelog entry:

• Avoid PHP 8.4 deprecations

Details

Fix the following deprecation messages when running typo3 cache:flush on console:

PHP Deprecated:  YoastSeoForTypo3\YoastSeo\Backend\PageLayoutHeader::render(): Implicitly marking parameter $params as nullable is deprecated, the explicit nullable type must be used instead in /var/www/html/vendor/yoast-seo-for-typo3/yoast_seo/Classes/Backend/PageLayoutHeader.php on line 27
PHP Deprecated:  YoastSeoForTypo3\YoastSeo\Controller\AbstractBackendController::returnResponse(): Implicitly marking parameter $moduleTemplate as nullable is deprecated, the explicit nullable type must be used instead in /var/www/html/vendor/yoast-seo-for-typo3/yoast_seo/Classes/Controller/AbstractBackendController.php on line 25
PHP Deprecated:  YoastSeoForTypo3\YoastSeo\EventListener\RecordCanonicalListener::__construct(): Implicitly marking parameter $recordService as nullable is deprecated, the explicit nullable type must be used instead in /var/www/html/vendor/yoast-seo-for-typo3/yoast_seo/Classes/EventListener/RecordCanonicalListener.php on line 16
PHP Deprecated:  YoastSeoForTypo3\YoastSeo\MetaTag\Generator\AbstractGenerator::__construct(): Implicitly marking parameter $managerRegistry as nullable is deprecated, the explicit nullable type must be used instead in /var/www/html/vendor/yoast-seo-for-typo3/yoast_seo/Classes/MetaTag/Generator/AbstractGenerator.php on line 19
PHP Deprecated:  YoastSeoForTypo3\YoastSeo\PageTitle\RecordPageTitleProvider::__construct(): Implicitly marking parameter $recordService as nullable is deprecated, the explicit nullable type must be used instead in /var/www/html/vendor/yoast-seo-for-typo3/yoast_seo/Classes/PageTitle/RecordPageTitleProvider.php on line 16
PHP Deprecated:  YoastSeoForTypo3\YoastSeo\Utility\JavascriptUtility::loadJavascript(): Implicitly marking parameter $pageRenderer as nullable is deprecated, the explicit nullable type must be used instead in /var/www/html/vendor/yoast-seo-for-typo3/yoast_seo/Classes/Utility/JavascriptUtility.php on line 13

Quality assurance

• I have tested this code to the best of my abilities
• I have added unittests to verify the code works as intended

[RinyVT]

Thanks for the PR!
This will be released with the new major release :)