[Php81] Fix property with attribute inlined on ReadOnlyPropertyRector

[samsonasik]

Given the following code:

    #[Serializer\Since(Option::SINCE_20211124)]
    private string $name;

It currently produce inlined readonly:

-    private readonly string $name;
+    #[Serializer\Since(Option::SINCE_20211124)]private readonly string $name;

which should be on next line of attribute. This PR try to fix it.

Fixes rectorphp/rector#7021

[samsonasik]

Fixed 🎉 /cc @reypm

[samsonasik]

All checks have passed 🎉 @TomasVotruba it is ready for review.

[TomasVotruba]

Thanks 👍