make ErrorResponse.Message non-nullable

Author: RenderMichael

dotnet/src/webdriver/ErrorResponse.cs

@@ -86,7 +86,7 @@ public ErrorResponse(Dictionary<string, object?>? responseValue)
         /// <summary>
         /// Gets or sets the message from the response
         /// </summary>
-        public string? Message { get; } = string.Empty;
+        public string Message { get; } = string.Empty;
 
         /// <summary>
         /// Gets or sets the class name that threw the error