Renamed a variable to explain better what it is

findTaggedServiceIds does not return an array of tag attributes. It returns an array of tags, each of them being an array of attributes.
This is necessary because a service can be tagged several times with the same tag (useful when attributes are used to configure the behavior of the tag, like for kernel.event_listener for instance).

As this bundle is build for a tutorial, it is important to avoid confusion in the naming IMO. I saw lots of compiler passes using attributes on a tag by naming it ``$attributes`` and then accessing ``$attributes[0]['event']``, thus ignoring tags except the first one. To be honest, this mistake was first done in the core itself by Fabien.

I suggest updating the code snippet in your AFSY article as well.