fix CI: unreachable warning make isInstanceOf test fail

Author: liufengyun

compiler/src/dotty/tools/dotc/reporting/diagnostic/messages.scala

@@ -910,7 +910,7 @@ object messages {
   case class MatchCaseUnreachable()(implicit ctx: Context)
   extends Message(MatchCaseUnreachableID) {
     val kind = "Match case Unreachable"
-    val msg = "unreachable code"
+    val msg = "unreachable case"
     val explanation = ""
   }
 

tests/pos-special/isInstanceOf/3324d.scala

@@ -3,6 +3,6 @@ class Test {
 
   x match {
     case _: List[Int @unchecked] => 5
-    case _: List[Int] @unchecked => 5
+    case _: Option[Int] @unchecked => 5
   }
 }

tests/pos-special/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 String      => // scalac emits a warning
     case _ =>
   }
 }