fix scala#11331

Author: rssh

compiler/src/dotty/tools/dotc/core/SymDenotations.scala

@@ -2207,7 +2207,9 @@ object SymDenotations {
       if !myCompanion.exists then
         ensureCompleted()
       myCompanion
-    override def registeredCompanion_=(c: Symbol) = { myCompanion = c }
+
+    override def registeredCompanion_=(c: Symbol) = 
+      myCompanion = c 
 
     private var myNestingLevel = -1
 
@@ -2457,6 +2459,7 @@ object SymDenotations {
       !owner.isClass
       || owner.isRefinementClass
       || owner.is(Scala2x)
+      || denot.is(Synthetic)
       || owner.unforcedDecls.contains(denot.name, denot.symbol)
       || denot.isSelfSym
       || denot.isLocalDummy)