Allow Symfony v7

[szepeviktor]

Description

Fulfill the promise of https://github.com/kreait/firebase-bundle/releases/tag/5.1.0

Checklist:

• [x] My code follows the style guidelines of this project
• [ ] I have performed a self-review of my own code
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I have made corresponding changes to the documentation

[jeromegamez]

Ooops 😅. Thank you!

[szepeviktor]

Glad to contribute.