Add relevant files to scala-steward config

[daddykotex]

This will avoid that our contributors have to spend time on things like: #42

[valencik]

In my experience this only works if your outer build also has the libraries of the inner build.

In typelevel.g8 we list all the inner dependencies in the outer build so they get steward updates:
https://github.com/typelevel/typelevel.g8/blob/main/build.sbt#L38-L48

[valencik]

Ahh, here's the reference I was trying to find:
scala-steward-org/scala-steward#1286 (comment)

[daddykotex]

oh thank you so much
I was thinking that the updates we were getting meant it was working, but we only got updates for the outer build (sbt, scalafmt)

nothing from the inner builds (even when the path were valid)

I'll address it
thanks