tests: Make 'publish' test umask-insensitive.

Fixes <https://bugs.gnu.org/47239

>.
Reported by Konrad Hinsen <konrad.hinsen@fastmail.net>.

* tests/publish.scm ("with cache"): Pass the result of 'stat:perms' to
'logand' to be umask-insensitive.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

tests/publish.scm

@@ -452,8 +452,8 @@ (define %gzip-magic-bytes
               (wait-for-file cached)
 
               ;; Both the narinfo and nar should be world-readable.
-              (= #o644 (stat:perms (lstat cached)))
-              (= #o644 (stat:perms (lstat nar)))
+              (= #o444 (logand #o444 (stat:perms (lstat cached))))
+              (= #o444 (logand #o444 (stat:perms (lstat nar))))
 
               (let* ((body         (http-get-port url))
                      (compressed   (http-get nar-url))