Add Jammy before upstream

See [0] for an older reference.

[0] https://git.launchpad.net/~cloudware/livecd-rootfs/+git/livecd-rootfs/commit/?id=c0df7db0b0d9459e14139f88905bce5d0bfe4c71

debian/changelog

@@ -1,3 +1,9 @@
+livecd-rootfs (2.742+1) jammy; urgency=medium
+
+  * Aadd jammy
+
+ -- Thomas Bechtold <thomas.bechtold@canonical.com>  Mon, 18 Oct 2021 14:06:31 +0200
+
 livecd-rootfs (2.742) impish; urgency=medium
 
   [ Brian Murray ]