Version 0.7.1 of the scala3-migrate-plugin requires version 4.7.8 of semanticdb-scalac, which doesn't exist for Scala 2.13.14+. Error message: (update) sbt.librarymanagement.ResolveException: Error downloading org.scalameta:semanticdb-scalac_2.13.15:4.7.8
Strangely enough, version 0.7.0 of sbt-scala3-migrate required version 4.9.9 of semanticdb-scalac, which is significantly more recent and works fine.
My test case
build.sbt
organization := "gael.renoux"
name := "gaston"
version := "1.0.0"
scalaVersion := "2.13.15"
scalacOptions ++= Seq("-Xsource:3")
project/plugins.sbt
addSbtPlugin("ch.epfl.scala" % "sbt-scala3-migrate" % "0.7.1")
project/build.properties