Change MiMa config in scala/scala to check against older versions too?

[SethTisue]

In scala/scala's project/MimaFilters.scala we currently have:

project/MimaFilters.scala:    mimaReferenceVersion := Some("2.13.9"),
project/MimaFilters.scala:    mimaPreviousArtifacts       := mimaReferenceVersion.value.map(organization.value % name.value % _).toSet,

Are we sure that we don't also need to check against 2.13.0, or against all previous 2.13.x versions? (And same on 2.12.x branch?)

I've opened lightbend-labs/mima#724 as a discussion on this for library maintainers generally, but I'm also opening this separate ticket, since the situation in scala/scala is a bit different than most libraries, since scala-library is checked for both forwards and backwards bincompat. Many library maintainers only maintain backwards bincompat.