Make sure update script of lantern.tasks only triggers if the table exists (async_tasks are enabled)

Author: Ngalstyan4

lantern_hnsw/sql/updates/0.5.0--0.6.0.sql

@@ -1,4 +1,9 @@
-ALTER TABLE lantern.tasks ADD COLUMN pg_cron_jobid bigint default null;
+DO $$
+BEGIN
+    IF EXISTS (SELECT 1 FROM information_schema.tables WHERE table_schema = 'lantern' AND table_name = 'tasks') THEN
+        ALTER TABLE lantern.tasks ADD COLUMN pg_cron_jobid bigint DEFAULT NULL;
+    END IF;
+END $$;
 CREATE OR REPLACE FUNCTION _lantern_internal.async_task_finalizer_trigger() RETURNS TRIGGER AS $$
 DECLARE
   res RECORD;