Fix ScalaSettings

Author: noti0na1

compiler/src/dotty/tools/dotc/config/ScalaSettings.scala

@@ -416,7 +416,7 @@ private sealed trait YSettings:
   // Experimental language features
   val YnoKindPolymorphism: Setting[Boolean] = BooleanSetting(ForkSetting, "Yno-kind-polymorphism", "Disable kind polymorphism.")
   val YexplicitNulls: Setting[Boolean] = BooleanSetting(ForkSetting, "Yexplicit-nulls", "Make reference types non-nullable. Nullable types can be expressed with unions: e.g. String|Null.")
-  val YnoFlexibleTypes: Setting[Boolean] = BooleanSetting("-Yno-flexible-types", "Disable turning nullable Java return types and parameter types into flexible types, which behaves like abstract types with a nullable lower bound and non-nullable upper bound.")
+  val YnoFlexibleTypes: Setting[Boolean] = BooleanSetting(ForkSetting, "-Yno-flexible-types", "Disable turning nullable Java return types and parameter types into flexible types, which behaves like abstract types with a nullable lower bound and non-nullable upper bound.")
   val YcheckInit: Setting[Boolean] = BooleanSetting(ForkSetting, "Ysafe-init", "Ensure safe initialization of objects.")
   val YcheckInitGlobal: Setting[Boolean] = BooleanSetting(ForkSetting, "Ysafe-init-global", "Check safe initialization of global objects.")
   val YrequireTargetName: Setting[Boolean] = BooleanSetting(ForkSetting, "Yrequire-targetName", "Warn if an operator is defined without a @targetName annotation.")