wait 10s before calculating next midnight for daily service

Discord logs the icon/name changes twice, with a different name each
time. The guild update service is likely running twice, possibly due to
faulty calculations of the next midnight - after the first run, it might
calculate a very short sleep period or none at all, only sleeping until
next midnight afterwards. The cause of this is unknown, but if it has to
do with system time, waiting for the 10 seconds might be enough to
let the system recognise the date change and allow it to sleep
for the proper ~24h.

src/discordbot/events/service.rs

@@ -8,6 +8,9 @@ use super::Event;
 pub async fn run_event_service(ctx: Context, guild_id: GuildId) {
     loop {
         update_guild(&ctx, guild_id).await.ok();
+
+        // make sure temporal boundaries have been cleared
+        tokio::time::sleep(std::time::Duration::from_secs(10)).await;
         sleep_until_next_midnight().await;
     }
 }