sourcehut: fix build on Darwin

Fix test failures by disabline tests that use multiprocessing. On
Darwin, multiprocessing uses `spawn` instead of `fork` by default,
resulting in test failures due to pickling errors.

pkgs/applications/version-management/sourcehut/default.nix

···
-{ python3
+{ lib
+, stdenv
+, python3
 , callPackage
 , recurseIntoAttrs
 , nixosTests
···
           hash = "sha256-aRO4JH2KKS74MVFipRkx4rQM6RaB8bbxj2lwRSAMSjA=";
         };
         nativeCheckInputs = with super; [ pytestCheckHook mock ];
-        disabledTestPaths = [];
+        disabledTestPaths = []
+          # Disable incompatible tests on Darwin.
+          ++ lib.optionals stdenv.isDarwin [ "test/aaa_profiling" ];
       });
 
       flask-sqlalchemy = super.flask-sqlalchemy.overridePythonAttrs (oldAttrs: rec {