Fix #12474: add regression test

Author: anatoliykmetyuk

tests/pos/i12474.scala

@@ -0,0 +1,17 @@
+package bugreport
+
+import scala.compiletime.erasedValue
+
+trait Show[A]:
+  def show(a: A): String
+
+inline def showTuple[Types]: Show[Types] =
+  inline erasedValue[Types] match
+    case _: (head *: tail) =>
+      val instance =
+        new Show[head *: tail]:
+          def show(tuple: head *: tail): String = "dummy"
+      instance.asInstanceOf[Show[Types]]
+
+@main def run() =
+  showTuple[(Int, Int)]