head-node: Update Cuirass URL.

* head-node.scm <unattended-upgrade-configuration>[channels]: Update
Cuirass URL.

head-node.scm

@@ -548,7 +548,7 @@ if ($http_user_agent ~~ \"(~a)\" ) {
                            (channels
                             #~(cons* (channel
                                       (name 'cuirass)
-                                      (url "https://git.savannah.gnu.org/git/guix/guix-cuirass.git")
+                                      (url "https://codeberg.org/guix/cuirass.git")
                                       (branch "main")
                                       (introduction
                                        (make-channel-introduction