Drop support of Symfony 5.4

[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)