fix extension test

Author: noti0na1

tests/explicit-nulls/pos/opaque-nullable.scala

@@ -10,15 +10,13 @@ object Nullable {
   def some[A <: AnyRef](x: A): Nullable[A] = x
   def none: Nullable[Nothing] = null
 
-  given nullableOps as AnyRef {
-    extension [A <: AnyRef](x: Nullable[A])
-      def isEmpty: Boolean = x == null
+  extension [A <: AnyRef](x: Nullable[A])
+    def isEmpty: Boolean = x == null
 
-    extension [A <: AnyRef, B <: AnyRef](x: Nullable[A])
-      def flatMap(f: A => Nullable[B]): Nullable[B] =
-        if (x == null) null
-        else f(x)
-  }
+  extension [A <: AnyRef, B <: AnyRef](x: Nullable[A])
+    def flatMap(f: A => Nullable[B]): Nullable[B] =
+      if (x == null) null
+      else f(x)
 
   val s1: Nullable[String] = "hello"
   val s2: Nullable[String] = null