fix: DisconnectAsync not disconnecting users (#2346)

src/Discord.Net.Rest/Entities/Guilds/RestGuild.cs

@@ -1404,7 +1404,7 @@ namespace Discord.Rest
         /// </summary>
         /// <param name="user">The user to disconnect.</param>
         /// <returns>A task that represents the asynchronous operation for disconnecting a user.</returns>
-        async Task IGuild.DisconnectAsync(IGuildUser user) => await user.ModifyAsync(x => x.Channel = new Optional<IVoiceChannel>());
+        async Task IGuild.DisconnectAsync(IGuildUser user) => await user.ModifyAsync(x => x.Channel = null);
 
         /// <inheritdoc />
         async Task<IGuildUser> IGuild.GetUserAsync(ulong id, CacheMode mode, RequestOptions options)

src/Discord.Net.WebSocket/Entities/Guilds/SocketGuild.cs

@@ -1407,7 +1407,7 @@ namespace Discord.WebSocket
         /// </summary>
         /// <param name="user">The user to disconnect.</param>
         /// <returns>A task that represents the asynchronous operation for disconnecting a user.</returns>
-        async Task IGuild.DisconnectAsync(IGuildUser user) => await user.ModifyAsync(x => x.Channel = new Optional<IVoiceChannel>());
+        async Task IGuild.DisconnectAsync(IGuildUser user) => await user.ModifyAsync(x => x.Channel = null);
         #endregion
 
         #region Stickers