Tighten condition when to check enum constructors

Fixes #11081

Author: odersky

compiler/src/dotty/tools/dotc/typer/Checking.scala

@@ -1193,7 +1193,7 @@ trait Checking {
         checkRefsLegal(tree, cdef.symbol, allowAccess, "enum case")
       }
 
-      if (stat.symbol.is(Case))
+      if (stat.symbol.isAllOf(EnumCase))
         stat match {
           case TypeDef(_, Template(DefDef(_, paramss, _, _), parents, _, _)) =>
             paramss.foreach(_.foreach(check))

tests/pos/i11081.scala

@@ -0,0 +1,5 @@
+enum Outer:
+  case Foo
+object Outer:
+  trait Bar
+  case class Baz(bar: Bar)