Wrap the PRAGMA statement in sqlalchemy.text.

SQLAlchemy 2 no longer supports raw strings passed to `.execute()`
methods.

platypush/plugins/entities/__init__.py

@@ -3,7 +3,7 @@ from threading import Thread
 from time import time
 from typing import Optional, Any, Collection, Mapping
 
-from sqlalchemy import or_
+from sqlalchemy import or_, text
 from sqlalchemy.orm import make_transient, Session
 
 from platypush.config import Config
@@ -198,7 +198,7 @@ class EntitiesPlugin(Plugin):
             if str(session.connection().engine.url).startswith('sqlite://'):
                 # SQLite requires foreign_keys to be explicitly enabled
                 # in order to proper manage cascade deletions
-                session.execute('PRAGMA foreign_keys = ON')
+                session.execute(text('PRAGMA foreign_keys = ON'))
 
             entities: Collection[Entity] = (
                 session.query(Entity).filter(Entity.id.in_(entities)).all()