cargo-raze: increase open file descriptors limits for tests on darwin

https://hydra.nixos.org/build/239024688/nixlog/2
https://hydra.nixos.org/build/239009073/nixlog/2
```
thread '<unnamed>' panicked at 'Cannot build local tokio runtime: Os { code: 24, kind: Uncategorized, message: "Too many open files" }', /private/tmp/nix-build-cargo-raze-0.16.0.drv-0/cargo-raze-0.16.0-vendor.tar.gz/httpmock/src/lib.rs:1436:14
```

Seems to be a typical darwin failure, some packages already bump
file descriptors limit to 1024 (same as default in some Linux distros,
default darwin value seems to be 256 these days)

Also has a report upstream
google/cargo-raze#544

ZHF: NixOS#265948

pkgs/development/tools/rust/cargo-raze/default.nix

@@ -31,6 +31,12 @@ rustPlatform.buildRustPackage rec {
   ]
   ++ lib.optional stdenv.isDarwin Security;
 
+  preCheck = lib.optionalString stdenv.isDarwin ''
+    # Darwin issue: Os { code: 24, kind: Uncategorized, message: "Too many open files" }
+    # https://github.com/google/cargo-raze/issues/544
+    ulimit -n 1024
+  '';
+
   __darwinAllowLocalNetworking = true;
 
   meta = with lib; {