Backport "Add regression tests" to LTS (#21066)

Backports #20177 to the LTS branch.

PR submitted by the release tooling.
[skip ci]

Author: WojciechMazur

tests/pos/i19749.scala

@@ -0,0 +1,15 @@
+import scala.deriving.Mirror
+
+case class A(x: Int, y: String)
+
+trait SomeTrait[T]
+
+object SomeTrait:
+  given [T]: SomeTrait[T] with {}
+
+def f1[T](using p: Mirror.ProductOf[T]): Tuple.Elem[p.MirroredElemTypes, 0] = ???
+
+def f2[T, R](f: T => R)(using SomeTrait[R]) = ???
+
+// Scala3.3 is fine, 3.4 has compilation errors, p MirroredElemTypes type is missing and has been changed to Nothing
+val x = f2(_ => f1[A])