gnu: mu: Adjust to new GLib version.

* gnu/packages/mail.scm (%mu-gtester-patch): New variable.
  (mu)[source]: Use it.

gnu/packages/mail.scm

@@ -306,6 +306,15 @@ can read the same mailbox from multiple computers.  It supports IMAP as REMOTE
 repository and Maildir/IMAP as LOCAL repository.")
     (license gpl2+)))
 
+(define %mu-gtester-patch
+  ;; Ensure tests have unique names, to placate GLib 2.6's gtester.
+  (origin
+    (method url-fetch)
+    (uri "https://github.com/djcb/mu/commit/b44039ed.patch")
+    (sha256
+     (base32
+      "165hryqqhx3wah8a4f5jaq465azx1pm9r4jid7880pys9gd88qlv"))))
+
 (define-public mu
   (package
     (name "mu")
@@ -317,7 +326,8 @@ repository and Maildir/IMAP as LOCAL repository.")
               (file-name (string-append "mu-" version ".tar.gz"))
               (sha256
                (base32
-                "0wj33pma8xgjvn2akk7khzbycwn4c9sshxvzdph9dnpy7gyqxj51"))))
+                "0wj33pma8xgjvn2akk7khzbycwn4c9sshxvzdph9dnpy7gyqxj51"))
+              (patches (list %mu-gtester-patch))))
     (build-system gnu-build-system)
     (native-inputs
      `(("pkg-config" ,pkg-config)