### Pull Request Checklist <!-- Please read CONTRIBUTING.rst before submitting your pull request --> * [ ] Pull request is based on the develop branch * [ ] Pull request includes a [changelog file](https://github.com/matrix-org/synapse/blob/master/CONTRIBUTING.rst#changelog) * [ ] Pull request includes a [sign off](https://github.com/matrix-org/synapse/blob/master/CONTRIBUTING.rst#sign-off)