Administrators using the Debian/Ubuntu packages from `packages.matrix.org`, please check [the relevant section in the upgrade notes](https://github.com/element-hq/synapse/blob/release-v1.126/docs/upgrade.md#change-of-signing-key-expiry-date-for-the-debianubuntu-package-repository) as we have recently updated the expiry date on the repository's GPG signing key. The old version of the key will expire on `2025-03-15`. - Fix wheel building configuration in CI by installing libatomic1. ([\#18212](https://github.com/element-hq/synapse/issues/18212), [\#18213](https://github.com/element-hq/synapse/issues/18213))