fix(FC2): change Category Type from String to Integer in Model

- Change the type of `Category` from `string` to `int` in `ChannelData` class.

System.Text.Json.JsonException: The JSON value could not be converted to System.String. Path: $.data.channel_data.category | LineNumber: 0 | BytePositionInLine: 2859.
 ---> System.InvalidOperationException: Cannot get the value of a token type 'Number' as a string.

Signed-off-by: CHEN, CHUN <[email protected]>

Models/FC2MemberData.cs

@@ -62,7 +62,7 @@ public class ChannelData
     public int? Interval { get; set; }
 
     [JsonPropertyName("category")]
-    public string Category { get; set; }
+    public int Category { get; set; }
 
     [JsonPropertyName("category_name")]
     public string CategoryName { get; set; }