Add `matrix-org-archive-keyring` package as `Recommends` (#15110)

This is so installations will pull in the keyring package, allowing us
to update the expiry time of the `packages.matrix.org` repository.

debian/changelog

@@ -1,3 +1,9 @@
+matrix-synapse-py3 (1.77.0ubuntu1) UNRELEASED; urgency=medium
+
+  * Add `matrix-org-archive-keyring` package as recommended.
+
+ -- Synapse Packaging team <packages@matrix.org>  Mon, 20 Feb 2023 15:41:41 +0000
+
 matrix-synapse-py3 (1.77.0) stable; urgency=medium
 
   * New Synapse release 1.77.0.

debian/control

@@ -37,6 +37,7 @@ Depends:
 # so we put perl:Depends in Suggests rather than Depends.
 Recommends:
  ${shlibs1:Recommends},
+ matrix-org-archive-keyring,
 Suggests:
  sqlite3,
  ${perl:Depends},