Drop support of Symfony <6.4

[Kocal]

To be discussed, but given https://symfony.com/releases/5.4:

• Latest patch version: 5.4.49
• Released on: November 2021
• End of bug fixes: November 2024
• End of security fixes: February 2029

I think we can drop the support of Symfony 5.4 for UX 3.x

[smnandre]

100% (at least in 3.x)

[Kocal]

Changed removing Symfony support for <6.4.
The LTS 6.4 is still maintained for November 2026/2027, and versions <6.4 are not maintained anymore.