Runtime "Duplicate in union" error after generating schema in Scala 3

[jchyb]

Hello! Thank you for maintaining this library. I found the following issue when trying to migrate a project to scala 3.

Minimization with scala-cli:

//> using scala "3.3.1"
//> using dep "com.sksamuel.avro4s:avro4s-core_3:5.0.9"
import com.sksamuel.avro4s.SchemaFor

object Repr {
  sealed trait A
  sealed trait B1 extends A
  sealed trait B2 extends A
  case class Test() extends B1 with B2

  def gen() = {
    println(SchemaFor[A].schema)
  }
}

object Main {
  def main(args: Array[String]): Unit = {
    Repr.gen()
  }
}

causes (on runtime):

Exception in thread "main" org.apache.avro.AvroRuntimeException: Duplicate in union:Repr.Test
        at org.apache.avro.Schema$UnionSchema.<init>(Schema.java:1238)
        at org.apache.avro.Schema.createUnion(Schema.java:251)
        at org.apache.avro.Schema.createUnion(Schema.java:256)
        at com.sksamuel.avro4s.avroutils.SchemaHelper$.createSafeUnion(SchemaHelper.scala:166)
        at com.sksamuel.avro4s.schemas.TypeUnions$.schema(unions.scala:26)
        at com.sksamuel.avro4s.schemas.MagnoliaDerivedSchemas.split(magnolia.scala:20)
        at com.sksamuel.avro4s.schemas.MagnoliaDerivedSchemas.split$(magnolia.scala:10)
        at com.sksamuel.avro4s.SchemaFor$.split(SchemaFor.scala:55)
        at Repr$.gen(repr.scala:12)
        at Main$.main(repr.scala:18)
        at Main.main(repr.scala)

When replacing scala version with 2.13, and using 4.1.1 version of the library, the schema is successfully generated:

[{"type":"record","name":"Test","namespace":"Repr","fields":[]}]