To my understanding, dependencies reside at project level and per-configuration dependencies only further constrain the dependency to subsets of the classpath.
It may be possible to force a cyclic dependency at classpath level, but I’d definitely steer clear of this. What remains of the concept of two separate projects if they are interdependent? Moving the shared parts to a dedicated upstream project seems to be the right choice here.
(I’d go even further and apply this rationale at the package level, as well, according to the Acyclic Dependencies Principle, which used to have some traction in the Java/OO space but doesn’t really seem to be a thing in the Scala camp - or maybe it is, but everybody just takes it for granted, so nobody talks about it much.)