Drop triggers loop fix (#252)

1) Postgres 16.1 throws an error:

```
NOTICE:  schema "grestv0" already exists, skipping
NOTICE:  web_anon exists, skipping...
NOTICE:  authenticator exists, skipping...
NOTICE:  role "authenticator" has already been granted membership in role "web_anon" by role "postgres"
NOTICE:  table "genesis" does not exist, skipping
NOTICE:  No fuctions found in schema grest
ERROR:  syntax error at or near "FOR"
LINE 1: FOR r IN (SELECT trigger_name, event_object_table FROM infor...
        ^
Exiting...
```

Author: xray-robot

files/grest/rpc/db-scripts/basics.sql

@@ -116,9 +116,17 @@ END
 $do$;
 
 -- DROP EXISTING GREST ADDED TRIGGERS ON PUBLIC SCHEMA
-FOR r IN (SELECT trigger_name, event_object_table FROM information_schema.triggers WHERE trigger_schema = 'public' AND action_statement LIKE '%grest.%') LOOP
-  EXECUTE 'DROP TRIGGER IF EXISTS ' || quote_ident(r.trigger_name) || ' ON ' || quote_ident(r.event_object_table);
-END LOOP;
+DO
+$$
+DECLARE
+  r record;
+BEGIN
+  FOR r IN (SELECT trigger_name, event_object_table FROM information_schema.triggers WHERE trigger_schema = 'public' AND action_statement LIKE '%grest.%')
+  LOOP
+    EXECUTE 'DROP TRIGGER IF EXISTS ' || quote_ident(r.trigger_name) || ' ON ' || quote_ident(r.event_object_table);
+  END LOOP;
+END
+$$;
 
 -- HELPER FUNCTIONS --
 CREATE FUNCTION grest.get_query_pids_partial_match(_query text)