Add test for #20342

Author: noti0na1

tests/pos/i20342.scala

@@ -0,0 +1,15 @@
+class Repo[EC, E](using defaults: RepoDefaults[EC, E])
+trait RepoDefaults[EC, E]
+object RepoDefaults:
+  inline given genImmutableRepo[E: DbCodec]: RepoDefaults[E, E] = ???
+  inline given genRepo[EC: DbCodec, E: DbCodec]: RepoDefaults[EC, E] = ???
+
+trait DbCodec[E]
+
+case class PersonCreator(name: String)
+case class Person(id: Long)
+given DbCodec[Person] = ???
+given DbCodec[PersonCreator] = ???
+
+@main def Test =
+  val personRepo = Repo[PersonCreator, Person]