use isPatternTypeSymbol to avoid duplicate

Author: liufengyun

compiler/src/dotty/tools/dotc/transform/IsInstanceOfChecker.scala

@@ -80,7 +80,7 @@ object Checkable {
     def replaceX(implicit ctx: Context) = new TypeMap {
       def apply(tp: Type) = tp match {
         case tref: TypeRef
-        if !tref.typeSymbol.isClass && tref.symbol.is(Case) =>
+        if isPatternTypeSymbol(tref.typeSymbol) =>
           if (variance == 1) tref.info.hiBound
           else if (variance == -1) tref.info.loBound
           else OrType(defn.AnyType, defn.NothingType)

tests/neg-custom-args/isInstanceOf/3324h.scala

@@ -2,7 +2,7 @@ object Test {
   trait Marker
   def foo[T](x: T) = x match {
     case _: (T & Marker)       => // no warning
-    // case _: T with Marker => // scalac emits a warning
+    case _: T with Marker      => // scalac emits a warning
     case _ =>
   }