docs: fixes comment for Responses property

src/Microsoft.OpenApi/Models/OpenApiOperation.cs

@@ -75,7 +75,7 @@
         public IOpenApiRequestBody? RequestBody { get; set; }
 
         /// <summary>
-        /// REQUIRED. The list of possible responses as they are returned from executing this operation.
+        /// The list of possible responses as they are returned from executing this operation.
         /// </summary>
         public OpenApiResponses? Responses { get; set; } = [];
 
@@ -226,7 +226,7 @@
         /// <summary>
         /// Serialize <see cref="OpenApiOperation"/> to Open Api v2.0.
         /// </summary>
         public virtual void SerializeAsV2(IOpenApiWriter writer)
         {
             Utils.CheckArgumentNull(writer);
 
@@ -336,7 +336,7 @@
 
                 writer.WriteOptionalCollection(OpenApiConstants.Schemes, schemes, (w, s) => 
                 {
                     if (!string.IsNullOrEmpty(s) && s is not null)
                     {
                         w.WriteValue(s);
                     }