### Pull Request Checklist

<!-- Please read CONTRIBUTING.md before submitting your pull request -->

* [ ] I have added any new tests that need to pass to `testfile` as specified in [docs/sytest.md](https://github.com/matrix-org/dendrite/blob/master/docs/sytest.md)
* [ ] I have made sure any new dependencies have been checked into the `vendor/` directory
* [ ] Pull request includes a [sign off](https://github.com/matrix-org/dendrite/blob/master/CONTRIBUTING.md#sign-off)