nix: fix installCheckPhase crashes on Darwin

While building nix on Darwin, I encountered an error in the `installCheckPhase`:

```
nix>     building '/private/tmp/nix-build-nix-2.17.1.drv-1/nix-test/tests/fetchurl/store/mkc9z3arar02wi5jii655cjhdinx4npy-fetchurl.sh.drv'...
nix>     waiting for children
nix>     building of '/private/tmp/nix-build-nix-2.17.1.drv-1/nix-test/tests/fetchurl/store/mkc9z3arar02wi5jii655cjhdinx4npy-fetchurl.sh.drv^out' from .drv file: read 377 bytes
nix>     objc[70707]: +[__NSCFConstantString initialize] may have been in progress in another thread when fork() was called.
nix>     objc[70707]: +[__NSCFConstantString initialize] may have been in progress in another thread when fork() was called. We cannot safely call it or ignore it in the fork() child process. Crashing instead. Set a breakpoint on objc_initializeAfterForkError to debug.
nix>     waiting for children
```

I noticed that #278802 should have addressed this problem, but it didn't.
The solution for me was to replace `yes` with `YES`.

As it turns out, most of the references to `OBJC_DISABLE_INITIALIZE_FORK_SAFETY` use `YES` instead of `yes`.

https://airflow.apache.org/blog/airflow-1.10.10/#running-airflow-on-macos
http://sealiesoftware.com/blog/archive/2017/6/5/Objective-C_and_fork_in_macOS_1013.html

The objective C code that parses the environment variable is defined in
the function `environ_init` in [here](https://github.com/opensource-apple/objc4/blob/cd5e62a5597ea7a31dccef089317abb3a661c154/runtime/objc-runtime.mm#L265) and it does
`*opt->var = (0 == strcmp(value, "YES"));`.

```
% nix-info -m
 - system: `"aarch64-darwin"`
 - host os: `Darwin 21.3.0, macOS 12.2.1`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.19.2`
 - channels(hetzner): `"darwin, nixpkgs-22.05-darwin"`
 - channels(root): `"darwin, nixpkgs-23.05-darwin"`
 - nixpkgs: `/Users/hetzner/git/nixpkgs`
```

0 files changed, 0 insertions, 0 deletions