fix error message test

Author: liufengyun

compiler/test/dotty/tools/dotc/reporting/ErrorMessagesTests.scala

@@ -824,13 +824,11 @@ class ErrorMessagesTests extends ErrorMessagesTest {
     checkMessagesAfter("refchecks") {
       """
         |object AnonymousF {
-        |  val f = { case l@List(1,2,3) => Some(l) }
+        |  val f = { case l@List(1,2,3) => Some(l); case _ => None }
         |}""".stripMargin
     }
     .expect { (ictx, messages) =>
       implicit val ctx: Context = ictx
-      val defn = ictx.definitions
-
       assertMessageCount(1, messages)
       val AnonymousFunctionMissingParamType(param, args, _, pt) :: Nil = messages
       assertEquals("x$1", param.show)