Fix typo in comment

Author: Michael Paquier <michael@paquier.xyz>

Author: mhagander

src/backend/access/transam/xlog.c

@@ -2157,7 +2157,7 @@ AdvanceXLInsertBuffer(XLogRecPtr upto, bool opportunistic)
 
 		/*
 		 * If online backup is not in progress, mark the header to indicate
-		 * that* WAL records beginning in this page have removable backup
+		 * that WAL records beginning in this page have removable backup
 		 * blocks.  This allows the WAL archiver to know whether it is safe to
 		 * compress archived WAL data by transforming full-block records into
 		 * the non-full-block format.  It is sufficient to record this at the