Fixed Typo (#29557)

when during a Challenge => during a Challenge

src/Security/Authentication/Cookies/src/CookieAuthenticationOptions.cs

@@ -99,8 +99,8 @@ namespace Microsoft.AspNetCore.Authentication.Cookies
 
         /// <summary>
         /// The ReturnUrlParameter determines the name of the query string parameter which is appended by the handler
-        /// when during a Challenge. This is also the query string parameter looked for when a request arrives on the
-        /// login path or logout path, in order to return to the original url after the action is performed.
+        /// during a Challenge. This is also the query string parameter looked for when a request arrives on the login
+        /// path or logout path, in order to return to the original url after the action is performed.
         /// </summary>
         public string ReturnUrlParameter { get; set; }