freeze gadt in both cases of isSubInfo

Author: Linyxus

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

@@ -1865,7 +1865,7 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
                   matchingMethodParams(info1, info2, precise = false)
                   && isSubInfo(info1.resultType, info2.resultType.subst(info2, info1), symInfo1.resultType)
                   && sigsOK(symInfo1, info2)
-                case _ => isSubType(info1, info2)
+                case _ => inFrozenGadtIf(tp1IsSingleton) { isSubType(info1, info2) }
             case _ => inFrozenGadtIf(tp1IsSingleton) { isSubType(info1, info2) }
 
         val info1 = m.info.widenExpr