PG: Only list tables where schema has USAGE permission (#7000)

This covers cases where partitioned tables are part of a schema that is
not accessible by the current user.

CREATE SCHEMA xyz;

CREATE TABLE xyz.tab (
   id bigint GENERATED ALWAYS AS IDENTITY,
   ts timestamp NOT NULL
) PARTITION BY LIST ((ts::date));

CREATE TABLE xyz.tab_default PARTITION OF xyz.tab DEFAULT;

redash/query_runner/pg.py

@@ -231,7 +231,9 @@ def _get_tables(self, schema):
         ON a.attrelid = c.oid
         AND a.attnum > 0
         AND NOT a.attisdropped
-        WHERE c.relkind IN ('m', 'f', 'p') AND has_table_privilege(s.nspname || '.' || c.relname, 'select')
+        WHERE c.relkind IN ('m', 'f', 'p')
+        AND has_table_privilege(s.nspname || '.' || c.relname, 'select')
+        AND has_schema_privilege(s.nspname, 'usage')
 
         UNION