Update license in Debian metadata (#16807)

debian/changelog

@@ -1,3 +1,9 @@
+matrix-synapse-py3 (1.99.0~rc1ubuntu1) UNRELEASED; urgency=medium
+
+  * Fix copyright file with new licensing
+
+ -- Synapse Packaging team <packages@matrix.org>  Thu, 11 Jan 2024 13:47:29 +0000
+
 matrix-synapse-py3 (1.99.0~rc1) stable; urgency=medium
 
   * New Synapse release 1.99.0rc1.

debian/copyright

@@ -6,6 +6,10 @@ Files: *
 Copyright: 2014-2017, OpenMarket Ltd, 2017-2018 New Vector Ltd
 License: Apache-2.0
 
+Files: *
+Copyright: 2023 New Vector Ltd
+License: AGPL-3.0-or-later
+
 Files: synapse/config/saml2.py
 Copyright: 2015, Ericsson
 License: Apache-2.0