Backport "Add regression test" to LTS (#20745)

Backports #18791 to the LTS branch.

PR submitted by the release tooling.
[skip ci]

Author: WojciechMazur

tests/pos/18789.scala

@@ -0,0 +1,4 @@
+sealed trait TypeId:
+  case class Foo() extends TypeId
+
+object TypeId {}