`jsonb-jackson` not automagically registering

[mechite]

jsonb-jackson has this clause:

provides io.avaje.jsonb.spi.JsonStreamFactory
with io.avaje.jsonb.jackson.JacksonAdapterFactory;

My jsonb msgpack implementation had this too, but doing Jsonb.instance() - I was getting the standard JSON adapter instead.

Going
from provides io.avaje.jsonb.spi.JsonStreamFactory
to provides io.avaje.jsonb.spi.JsonbExtension
solved the issue.

---

In io.avaje.jsonb.core.ExtensionLoader, we do
ServiceLoader.load(JsonbExtension.class ...
and downcast from there.

I believe that means that jsonb-jackson will no longer automagically register.
Can (and should) we write a test for the automatic registering, too?