gnu-maintenance: Do not look for releases in "w32" sub-directories.

* guix/gnu-maintenance.scm (latest-release): Filter out "w32"
directories.

guix/gnu-maintenance.scm

@@ -354,11 +354,14 @@ (define (file->source directory file)
       (let* ((entries (ftp-list conn directory))
 
              ;; Filter out sub-directories that do not contain digits---e.g.,
-             ;; /gnuzilla/lang and /gnupg/patches.
+             ;; /gnuzilla/lang and /gnupg/patches.  Filter out "w32"
+             ;; directories as found on ftp.gnutls.org.
              (subdirs (filter-map (match-lambda
                                     (((? patch-directory-name? dir)
                                       'directory . _)
                                      #f)
+                                    (("w32" 'directory . _)
+                                     #f)
                                     (((? contains-digit? dir) 'directory . _)
                                      dir)
                                     (_ #f))