fix TraceableResponseForV4::getInfo to be compatible with symfony-contracts in symfony-sentry 5.0.0

[jeslopcru]

Hi!
I found this issue #834 about a wrong signature in method getInfo
on Sentry\SentryBundle\Tracing\HttpClient\TraceableResponseForV4 using version 5.0.0.

Here you can see the change to make compatible the method.

I hope that it will help, let me know if you need any update

[Jean85]

I approved the CI just to show how this change is not feasible: this bundle supports back to PHP 7.2, so mixed is not allowed.

Thanks to PHP 7.2 having partial type widening though, this is perfectly valid code.

[Jean85]

Thanks for the contribution anyway.

[jeslopcru]

Thanks for the explanation! I will figure out how to fix my code to avoid this issue

Edited:
Brief explanation about what was wrong in my project in the issue