Exclude synthetic opaque proxy from lint (scala#24264)

Fixes scala#24263
[Cherry-picked 55f235c]

Author: som-snytt

tests/warn/i24263.scala

@@ -0,0 +1,6 @@
+//> using options -Werror -Wunused:all
+
+object test {
+  def f(t: Tuple): Nothing = ???
+  val _ = (inputTuple: NamedTuple.NamedTuple[Tuple, Tuple]) => f(inputTuple)
+}