Bump Symfony version

[kiler129]

Bump described symfony versions based on https://symfony.com/releases

However, overall, shouldn't the docs be changed to direct users to check https://symfony.com/releases instead of hardcoding things like:

Nowadays this is the 5.4 branch. If you are instead documenting a new feature, switch to the first Symfony version that included it, e.g. upstream/6.2.

WDYT?

[javiereguiluz]

Thanks!