Fix registering doctrine subscriber for kernel 6 with doctrine-bridge 7

[core23]

Fixes #28 when using symfony/doctrine-bridge v7 with symfony/http-kernel v6.

The doctrine.event_subscriber is deprecated since symfony 6.3:

User Deprecated: Since symfony/doctrine-bridge 6.3: Using Doctrine subscribers as services is deprecated, declare listeners instead

[core23]

Can you please double check @Zombaya?

[Zombaya]

I'm afraid I will not merge your MR, since in my opinion it's trying to solve the wrong problem(s).

1. Mixed symfony-versions are not recommended

You should not be using multiple versions of symfony together. The recommended way to do this is to use symfony/flex, which is available since symfony 4.0.

I'm not sure where it is documented on how to enable it, but it shows on the documention on how to upgrade a major version how you can upgrade from one version to the next:

# composer.json

"extra": {
      "symfony": {
           "allow-contrib": false,
-          "require": "6.4.*"
+          "require": "7.0.*"
      }
  }

2. Symfony 7.x should use attributes

When using symfony 7.x, we will be using attributes and will register ourselves as listeners instead of subscribers. We will not trigger the deprecation notice.

Conclusion

As I think this problem will be solved when using a single version of symfony, I will not be merging in this MR.

If this problem would trigger when exclusively using symfony 6.x, then I'd be willing to re-investigate.