Updated the composer.json to support symfony 7.0 and still support 6.4 .

[robert-sykes]

This addition adds a OR support for 7.0 of the symfony framework.

For example;

symfony/config:^6.4 causes an error on composer require if the project has a lock of symfony/config:^7.0 so the package can't be required into any projects that are currently set up to use 7.0.

This change adds it as a supported option so it can be installed by those projects.

[Ferror]

Thanks @robert-sykes for contribution. I will make sure via CI that it runs alright 😄