[FEATURE] - PHP 8.4 fixes

[dingo-d]

I noticed I got several deprecation notices while running some WPCLI scripts, for instance:

PHP Deprecated: EightshiftLibs\Cache\AbstractManifestCache::getCacheTopItem(): Implicitly marking parameter $fallback as nullable is deprecated, the explicit nullable type must be used instead
PHP Deprecated: EightshiftLibs\Helpers\ShortcodeTrait::getShortcode(): Implicitly marking parameter $content as nullable is deprecated, the explicit nullable type must be used instead
PHP Deprecated: EightshiftLibs\Main\Autowiring::setManifestCache(): Implicitly marking parameter $manifestCache as nullable is deprecated, the explicit nullable type must be used instead

You should run the automated tools to check for these and make a bc compatible fix.