Adds Symfony 6 support.

[iisisrael]

Co-authored-by: Aaron Opela [email protected]

[iisisrael]

If keeping support for older PHP versions is important, we can instead add checks for method exists, adding deprecation messages. It's only a concern in tests (Assert::assertMatchesRegularExpression()).

[GuilhemN]

Do you have a strong use case for this? A legacy app that you cannot easily update?

This library is not really maintained anymore I'd say, last update is from 2021.

If you can, I would rather suggest to move your app to a different OAuth client (see https://oauth.net/code/php/ for some examples), and we probably should consider deprecating this library.

[GuilhemN]

Probably decision here should be synced with https://github.com/FriendsOfSymfony/FOSOAuthServerBundle/issues/698.