Fixed #21452 -- Non-autocommit connections to PostgreSQL.

When settings.DATABASES['default']['AUTOCOMMIT'] = False, the connection
wasn't in autocommit mode but Django pretended it was.

Thanks Anssi for analysing this issue.

Refs #17062.

django/db/backends/postgresql_psycopg2/base.py

@@ -142,11 +142,11 @@ class DatabaseWrapper(BaseDatabaseWrapper):
                 conn_tz = get_parameter_status('TimeZone')
 
             if conn_tz != tz:
-                # Set the time zone in autocommit mode (see #17062)
-                self.set_autocommit(True)
                 self.connection.cursor().execute(
                     self.ops.set_time_zone_sql(), [tz]
                 )
+                # Commit after setting the time zone (see #17062)
+                self.connection.commit()
         self.connection.set_isolation_level(self.isolation_level)
 
     def create_cursor(self):