describe: In 'channels' format, quote the channel name.

Fixes a regression introduced in
commit 8548f995.

* guix/scripts/describe.scm (channel->sexp): Quote the channel name.

guix/scripts/describe.scm

@@ -89,7 +89,7 @@ (define (display-package-search-path fmt)
 
 (define (channel->sexp channel)
   `(channel
-    (name ,(channel-name channel))
+    (name ',(channel-name channel))
     (url ,(channel-url channel))
     (commit ,(channel-commit channel))))