[Robot] Add missing json error (#2326)

* Add 50600 Error code

* Update src/Discord.Net.Core/DiscordErrorCode.cs

Co-authored-by: Discord.Net Robot <robot@elons.sweatshop.stop>
Co-authored-by: Quin Lynch <49576606+quinchs@users.noreply.github.com>

src/Discord.Net.Core/DiscordErrorCode.cs

@@ -165,6 +165,7 @@ namespace Discord
         #endregion
 
         #region 2FA (60XXX)
+        MissingPermissionToSendThisSticker = 50600,
         Requires2FA = 60003,
         #endregion