Fix NLS for incorrect GUC enum value hint message

The translation markers were applied at the wrong place, so no string
was extracted for translation.

Also add translator comments here and in a similar place.

Reviewed-by: Álvaro Herrera <alvherre@kurilemu.de>
Discussion: https://www.postgresql.org/message-id/2c961fa1-14f6-44a2-985c-e30b95654e8d%40eisentraut.org

src/backend/replication/logical/relation.c

@@ -249,6 +249,7 @@ logicalrep_get_attrs_str(LogicalRepRelation *remoterel, Bitmapset *atts)
 	{
 		attcnt++;
 		if (attcnt > 1)
+			/* translator: This is a separator in a list of entity names. */
 			appendStringInfoString(&attsbuf, _(", "));
 
 		appendStringInfo(&attsbuf, _("\"%s\""), remoterel->attnames[i]);