python3Packages.flask-sqlalchemy: disable failing test

pkgs/development/python-modules/flask-sqlalchemy/default.nix

···
   disabledTests = [
     # flaky
     "test_session_scoping_changing"
+    # https://github.com/pallets-eco/flask-sqlalchemy/issues/1084
+    "test_persist_selectable"
   ];
 
   meta = with lib; {