python3Packages.msgpack: be mindful of borgbackup via passthru.tests

Unfortunately, BorgBackup, a backupping software is very sensible to MsgPack versions
to the extent of pinning patch-level versions…

I believe it's not totally absurd if they do it as they seems to consider it dangerous to
do otherwise.

As a result, I would like to ensure that python3Packages.msgpack are gated with that piece
of software ; of course, in case of security updates, we can consider extracting the patches
if reasonable or just breaking all dependents.

pkgs/development/python-modules/msgpack/default.nix

···
 , pytestCheckHook
 , pythonOlder
 , setuptools
+, borgbackup
 }:
 
 buildPythonPackage rec {
···
   pythonImportsCheck = [
     "msgpack"
   ];
+
+  passthru.tests = {
+    # borgbackup is sensible to msgpack versions: https://github.com/borgbackup/borg/issues/3753
+    # please be mindful before bumping versions.
+    inherit borgbackup;
+  };
 
   meta = with lib;  {
     description = "MessagePack serializer implementation";