Log message improvement

This log message implies all these changes will be applied.
But with high lag, that might not happen.
Clarify the log message

Author: amandasaurus

scripts/osm2pgsql-replication

@@ -517,7 +517,7 @@ def update(props, args):
         return 0
 
     remote_server_age_sec = int((dt.datetime.now(dt.timezone.utc) - current.timestamp).total_seconds())
-    LOG.debug("Applying %d sequence(s) (%d → %d), covering %s (%s sec) of changes (%s → %s)",
+    LOG.debug("Need to apply %d sequence(s) (%d → %d), covering %s (%s sec) of changes (%s → %s)",
         current.sequence - seq, current.sequence, seq,
         pretty_format_timedelta((current.timestamp - ts).total_seconds()),
         int((current.timestamp - ts).total_seconds()),