Fix `DiscordRestClient.GetChannelAsync` not getting forum channel

src/Discord.Net.Rest/Entities/Channels/RestChannel.cs

@@ -30,13 +30,15 @@ namespace Discord.Rest
                 ChannelType.Stage or
                 ChannelType.NewsThread or
                 ChannelType.PrivateThread or
-                ChannelType.PublicThread
+                ChannelType.PublicThread or
+                ChannelType.Forum
                     => RestGuildChannel.Create(discord, new RestGuild(discord, model.GuildId.Value), model),
                 ChannelType.DM or ChannelType.Group => CreatePrivate(discord, model) as RestChannel,
                 ChannelType.Category => RestCategoryChannel.Create(discord, new RestGuild(discord, model.GuildId.Value), model),
                 _ => new RestChannel(discord, model.Id),
             };
         }
+
         internal static RestChannel Create(BaseDiscordClient discord, Model model, IGuild guild)
         {
             return model.Type switch
@@ -47,7 +49,8 @@ namespace Discord.Rest
                 ChannelType.Stage or
                 ChannelType.NewsThread or
                 ChannelType.PrivateThread or
-                ChannelType.PublicThread
+                ChannelType.PublicThread or
+                ChannelType.Forum
                     => RestGuildChannel.Create(discord, guild, model),
                 ChannelType.DM or ChannelType.Group => CreatePrivate(discord, model) as RestChannel,
                 ChannelType.Category => RestCategoryChannel.Create(discord, guild, model),

src/Discord.Net.Rest/Entities/Channels/RestForumChannel.cs

@@ -41,9 +41,9 @@ namespace Discord.Rest
 
         }
 
-        internal new static RestStageChannel Create(BaseDiscordClient discord, IGuild guild, Model model)
+        internal new static RestForumChannel Create(BaseDiscordClient discord, IGuild guild, Model model)
         {
-            var entity = new RestStageChannel(discord, guild, model.Id);
+            var entity = new RestForumChannel(discord, guild, model.Id);
             entity.Update(model);
             return entity;
         }
@@ -66,6 +66,13 @@ namespace Discord.Rest
             ).ToImmutableArray();
         }
 
+        /// <inheritdoc/>
+        public async Task ModifyAsync(Action<ForumChannelProperties> func, RequestOptions options = null)
+        {
+            var model = await ForumHelper.ModifyAsync(this, Discord, func, options);
+            Update(model);
+        }
+
         /// <inheritdoc cref="IForumChannel.CreatePostAsync(string, ThreadArchiveDuration, int?, string, Embed, RequestOptions, AllowedMentions, MessageComponent, ISticker[], Embed[], MessageFlags)"/>
         public Task<RestThreadChannel> CreatePostAsync(string title, ThreadArchiveDuration archiveDuration = ThreadArchiveDuration.OneDay, int? slowmode = null, string text = null, Embed embed = null, RequestOptions options = null, AllowedMentions allowedMentions = null, MessageComponent components = null, ISticker[] stickers = null, Embed[] embeds = null, MessageFlags flags = MessageFlags.None)
             => ThreadHelper.CreatePostAsync(this, Discord, title, archiveDuration, slowmode, text, embed, options, allowedMentions, components, stickers, embeds, flags);