Address ifdef problem with macOS/BSD sandboxing (backport #13455)

[mergify]

Motivation

This PR addresses an issue we identified for macOS users. The #ifdef condition seems impossible, and causes some (but not all) builds to fail.

Based on git bisecting, it looks like this was introduced in #13281.

Context

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This is an automatic backport of pull request #13455 done by [Mergify](https://mergify.com).

[mergify]

This pull request has been removed from the queue for the following reason: pull request dequeued.

Pull request #13458 has been dequeued. The pull request could not be merged. This could be related to an activated branch protection or ruleset rule that prevents us from merging. (details: Required status check "tests on ubuntu" is in progress.).

You should look at the reason for the failure and decide if the pull request needs to be fixed or if you want to requeue it.
If you do update this pull request, it will automatically be requeued once the queue conditions match again.
If you think this was a flaky issue instead, you can requeue the pull request, without updating it, by posting a @mergifyio requeue comment.

[nixos-discourse]

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/critical-security-issue-in-nix-2-30-on-macos/66506/4