proper db.transaction_lock instead of adhoc clone (amending 2df0f3604a67);

--- a/src/Pure/General/sql.scala	Sun Jul 16 09:54:55 2023 +0200
+++ b/src/Pure/General/sql.scala	Sun Jul 16 10:50:40 2023 +0200
@@ -257,7 +257,7 @@
       create: Boolean = false,
       synchronized: Boolean = false,
     )(body: => A): A = {
-      def run: A = db.transaction { tables.lock(db, create = create); body }
+      def run: A = db.transaction_lock(tables, create = create)(body)
       if (synchronized) db.synchronized { run } else run
     }