Skip refreshing roles if the member is role-muted (#118)

Closes #116

src/Services/GuildDataService.cs

@@ -110,11 +110,14 @@ public sealed class GuildDataService : IHostedService
                 continue;
             }
 
+            if (data.MutedUntil is null)
+            {
                 var memberResult = await _guildApi.GetGuildMemberAsync(guildId, data.Id.ToSnowflake(), ct);
                 if (memberResult.IsSuccess)
                 {
                     data.Roles = memberResult.Entity.Roles.ToList().ConvertAll(r => r.Value);
                 }
+            }
 
             memberData.Add(data.Id, data);
         }