Update: Bump the bundle to Symfony 8 / PHP 8.4 (Case 212955)

[janopae]

Widen all symfony/* constraints to ^8.0, raise the PHP floor to ^8.4 (Symfony 8 requires PHP >= 8.4.1), and raise the CI PHP version to 8.4. Bump doctrine/doctrine-bundle to ^3.0 — v2.x has no Symfony 8 support.

Six additional code fixes were needed to stay green on Symfony 8:

• WebfactoryNewsletterRegistrationExtension::load(): add missing : void return type (Symfony 8 made ExtensionInterface::load() strict).
• Callback constraint: array-key constructor syntax (['callback' => ...]) was removed; pass the callable directly instead.
• Choice constraint: array options constructor was removed; use named arguments (choices:, multiple:, min:).
• Doctrine test config: auto_generate_proxy_classes removed from DoctrineBundle 3's ORM configuration tree.
• AppClassTemplatesTest: call $config->enableNativeLazyObjects(true) — Symfony 8 dropped the LazyGhostTrait that Doctrine ORM's old file-based proxy system relied on; PHP 8.4 native lazy objects replace it.
• All four Foundry factories: PersistentProxyObjectFactory → PersistentObjectFactory — the proxy mechanism is gone in Symfony 8.