I think this is a simple umask issue. Making the test check for just the bits worked for me:

diff --git a/tests/publish.scm b/tests/publish.scm
index 52101876b5..3e67c435ac 100644
--- a/tests/publish.scm
+++ b/tests/publish.scm
@@ -452,8 +452,8 @@ References: ~%"
(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))