channels.scm: Update Cuirass channel URL.

* channels.scm: Update Cuirass channel URL.

channels.scm

 (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