Support `sensio/framework-extra-bundle:^6`

[Marco Pivetta]

This is mostly a placeholder, potentially fixed by @dependabot upgrades (see #16 (review)), but in:

uuid-extra-bundle/composer.json

Lines 10 to 11 in 3744cf9

 "symfony/framework-bundle": "^3.0|^4.0|^5.0", 
 "sensio/framework-extra-bundle": "^3.0|^4.0|^5.0", 

It would be a good idea to:

• add symfony/*:^6 support
• drop symfony/*:^3 and symfony/*:^4 support (old versions still work, no?)

[Fred Cox]

closed by #18