Small SQL formatting fix in tutorial

Found a small formatting slip while I was going through the tutorial, so I changed the line to be consistent with the rest of the SQL syntax.

docs/tutorial/tests.rst

@@ -270,7 +270,7 @@ messages.
 
         with app.app_context():
             assert get_db().execute(
-                "select * from user where username = 'a'",
+                "SELECT * FROM user WHERE username = 'a'",
             ).fetchone() is not None