fix: references callback writer

Signed-off-by: Vincent Biret <[email protected]>

Author: baywet

src/Microsoft.OpenApi/Models/OpenApiReference.cs

@@ -158,11 +158,11 @@ public OpenApiReference(OpenApiReference reference)
         /// </summary>
         public void SerializeAsV31(IOpenApiWriter writer)
         {
-            SerializeInternal(writer, x =>
+            SerializeInternal(writer, w =>
             {
                 // summary and description are in 3.1 but not in 3.0
-                writer.WriteProperty(OpenApiConstants.Summary, Summary);
-                writer.WriteProperty(OpenApiConstants.Description, Description);
+                w.WriteProperty(OpenApiConstants.Summary, Summary);
+                w.WriteProperty(OpenApiConstants.Description, Description);
             });
         }