Allow Symfony 6

[bocharsky-bw]

Closes #457

[welcoMattic]

What it this?

[bocharsky-bw]

Ha, good question! Well, I see we use that bundle in deps list... and lately I start seeing this:

# composer update
bamarni/composer-bin-plugin contains a Composer plugin which is currently not in your allow-plugins config. See https://getcomposer.org/allow-plugins
Do you trust "bamarni/composer-bin-plugin" to execute code and wish to enable it now? (writes "allow-plugins" to composer.json) [y,n,d,?]

And I just replied Y, and it added this config. Without this little config it will always ask that message on each composer update/install command run. Any idea what else can we do? :)

[rvanlaak]

Was introduced by @Nyholm in #429 while adding github actions, but I'm not sure either why it is needed. So, I'm fine with allowing it for now.

[bocharsky-bw]

Thank you guys!