- Remove old admin API `GET /_synapse/admin/v1/users/<user_id>`. ([\#9401](https://github.com/matrix-org/synapse/issues/9401))
- Make `/_matrix/client/r0/register` expect a type of `m.login.application_service` when an Application Service registers a user, to align with [the relevant spec](https://spec.matrix.org/unstable/application-service-api/#server-admin-style-permissions). ([\#9548](https://github.com/matrix-org/synapse/issues/9548))
- Replace deprecated `imp` module with successor `importlib`. Contributed by Cristina Muñoz. ([\#9718](https://github.com/matrix-org/synapse/issues/9718))
Internal Changes
----------------
- Replace deprecated `imp` module with successor `importlib`. Contributed by Cristina Muñoz. ([\#9718](https://github.com/matrix-org/synapse/issues/9718))
- Experiment with GitHub Actions for CI. ([\#9661](https://github.com/matrix-org/synapse/issues/9661))
- Introduce flake8-bugbear to the test suite and fix some of its lint violations. ([\#9682](https://github.com/matrix-org/synapse/issues/9682))
- Update `scripts-dev/complement.sh` to use a local checkout of Complement, allow running a subset of tests and have it use Synapse's Complement test blacklist. ([\#9685](https://github.com/matrix-org/synapse/issues/9685))
