Fix #7424: add test

Author: liufengyun

tests/run/i7424/Enum_1.scala

@@ -0,0 +1,3 @@
+enum A {
+  case A1
+}

tests/run/i7424/Test_2.scala

@@ -0,0 +1,5 @@
+object Test {
+  def main(args: Array[String]): Unit = {
+    println(A.values)
+  }
+}