make sure it works with Scala 3

Author: romanowski

modules/tasty-lib/src/main/scala/scala/build/tastylib/TastyVersions.scala

@@ -16,7 +16,7 @@ object TastyVersions {
     scalaVersion: String,
     scalaCliVersion: String
   ): Either[String, Boolean] =
-    if (!scalaVersion.startsWith("3.")) Right(false)
+    if (!scalaVersion.startsWith("3.") && scalaVersion != "3" ) Right(false)
     else
       scalaVersion.split('.')(1).toInt match {
         case scalaMinor if scalaMinor > LatestSupportedScala.MinorVersion =>