use sa20 syntax

lib/galaxy/managers/users.py

@@ -20,6 +20,7 @@
     and_,
     exc,
     func,
+    select,
     true,
 )
 from sqlalchemy.orm.exc import NoResultFound
@@ -843,7 +844,8 @@ def get_user_by_username(app, username):
     """Get a user from the database by username."""
     sa_session = app.model.session
     try:
-        user = sa_session.query(app.model.User).filter(app.model.User.table.c.username == username).one()
+        stmt = select(model.User).filter(model.User.username == username)
+        user = session.execute(stmt).scalar_one()
         return user
     except Exception:
         return None