Add regression tests

Closes scala#9891

Author: nicolasstucki

tests/pos-macros/i9891.scala

@@ -0,0 +1,7 @@
+import scala.quoted._
+import scala.deriving.Mirror
+def derived[T: Type](using Quotes): Expr[Any] = {
+  val ev1: Expr[Mirror.Of[T]] = Expr.summon[Mirror.Of[T]].get
+  val ev2: Expr[Mirror.Of[T]] = Expr.summon(using Type.of[Mirror.Of[T]]).get
+  '{null}
+}