Symfony version(s) affected: 5.0.8, up to 5.2.3

Description
While trying to implement a Messenger transport, I'm having an issue with the local container dump, because I'm getting a mangled array of options, with strange values.

How to reproduce
The reproducer is this commit: Jean85/symfony-config-bug-repro@6bcb2dc

To reproduce:

• Clone https://github.com/Jean85/symfony-config-bug-repro
• composer install
• bin/console messenger:consume --env=test

It will die with a dump of the received options, which are:

[
  "queues" => [
    "q-receiver" => null
  ]
  0 => "something"
  "transport_name" => "receiver"
]

Instead of the expected:

[
  "queue_name" => "something"
  "transport_name" => "receiver"
]

I'm not sure if this is a bug localized to the Messenger and how it's configuration is handled in the FrameworkBundle, or it's somewhere else.