manifests that Namers.mkTypeCompleter is flag-agnostic

When introducing `FlagAgnosticCompleter` and `FlagAssigningCompleter`,
I have overlooked the completers created in namers. These completers
only assign type signatures, not flags, because they are only created
for symbols originating from sources and such symbols have their flags
assigned based on modifiers and source def trees when they are entered.

Author: xeno-by

src/compiler/scala/tools/nsc/typechecker/Namers.scala

@@ -1595,7 +1595,7 @@ trait Namers extends MethodSynthesis {
     val tree: Tree
   }
 
-  def mkTypeCompleter(t: Tree)(c: Symbol => Unit) = new LockingTypeCompleter {
+  def mkTypeCompleter(t: Tree)(c: Symbol => Unit) = new LockingTypeCompleter with FlagAgnosticCompleter {
     val tree = t
     def completeImpl(sym: Symbol) = c(sym)
   }