[Routing] allow setting multiple envs in #[Route] attribute

[santysisi]

Q	A
Branch?	7.4
Bug fix?	no
New feature?	yes
Deprecations?	yes
Issues	Fix #61344
License	MIT

Summary

This PR enhances the Symfony\Component\Routing\Attribute\Route attribute by allowing the env parameter to accept an array of environment names. This change enables defining a single route that is conditionally available in multiple environments without duplicating route definitions.

Before

To make a route available in both dev and test environments, two separate route attributes were needed:

#[Route('/test', name: 'test', env: 'dev')] #[Route('/test', name: 'test-testing', env: 'test')]

After

Now, the same can be achieved with a single attribute by passing an array:

#[Route('/test', name: 'test', env: ['dev', 'test'])]

[santysisi]

I'm not entirely sure if this qualifies as a breaking change 🤔
If it is, I can update the UPGRADE.md and change the target branch from 7.4 to 8.0.

[santysisi]

I believe the errors in this PR will be resolved by PR #61360 😄.

[santysisi]

I think the errors aren't relevant in the context of this PR

[santysisi]

@GromNaN Thanks a lot for all your suggestions! I’ve made the changes ❤️

[nicolas-grekas]

Why do we have setters at all?

[santysisi]

I think adding the setter helps keep consistency with the current class design. But if you feel it’s unnecessary, I can remove it
just let me know 🫡

[santysisi]

Thanks for the suggestions! 🙌
I’ve made the changes

[nicolas-grekas]

Thank you @santysisi.