Treat 3.5-migration the same as 3.5 for a warning

Treat 3.5-migration the same as 3.5 for a warning about implicit priority change

Fixes #20420

Author: odersky

tests/warn/i20420.scala

@@ -0,0 +1,27 @@
+//> using options -source 3.5-migration
+
+final class StrictEqual[V]
+final class Less[V]
+type LessEqual[V] = Less[V] | StrictEqual[V]
+
+object TapirCodecIron:
+  trait ValidatorForPredicate[Value, Predicate]
+  trait PrimitiveValidatorForPredicate[Value, Predicate]
+      extends ValidatorForPredicate[Value, Predicate]
+
+  given validatorForLessEqual[N: Numeric, NM <: N](using
+      ValueOf[NM]
+  ): PrimitiveValidatorForPredicate[N, LessEqual[NM]] = ???
+  given validatorForDescribedOr[N, P](using
+      IsDescription[P]
+  ): ValidatorForPredicate[N, P] = ???
+
+  trait IsDescription[A]
+  object IsDescription:
+    given derived[A]: IsDescription[A] = ???
+
+@main def Test = {
+  import TapirCodecIron.{*, given}
+  type IntConstraint = LessEqual[3]
+  summon[ValidatorForPredicate[Int, IntConstraint]] // warn
+}