Support Symfony 6

[eerison]

I can see other deprecations messages related with SentryBundle, in different files.
do you prefer to open one PR resolving all deprecations or one pr by file?

[Jean85]

One single PR is fine if the only needed change is a return/argument type.
We just need to check not to break backward compatibility.

[ste93cry]

Recently, we released some small enhancements as part of the next patch version, however I'm not sure it's correct nor that we should do this in this case as the scope looks a lot bigger and we didn't even started looking at supporting PHP 8.1. Opinions?

[Jean85]

8.1 was started in #559.

As for the scope, I expect those deprecations to provoke one-line diff each, so it shouldn't be so much stuff for a single PR.