package.nix: Apply OBJC_DISABLE_INITIALIZE_FORK_SAFETY workaround

This was previously already used in the launchd configuration for
nix-daemon.

(cherry picked from commit 855741aea57cd413a5da524169794a6790162d18)

package.nix

@@ -349,9 +349,15 @@ in {
 
   # Needed for tests if we are not doing a build, but testing existing
   # built Nix.
-  preInstallCheck = lib.optionalString (! doBuild) ''
-    mkdir -p src/nix-channel
-  '';
+  preInstallCheck =
+    lib.optionalString (! doBuild) ''
+      mkdir -p src/nix-channel
+    ''
+    # See https://github.com/NixOS/nix/issues/2523
+    # Occurs often in tests since https://github.com/NixOS/nix/pull/9900
+    + lib.optionalString stdenv.hostPlatform.isDarwin ''
+      export OBJC_DISABLE_INITIALIZE_FORK_SAFETY=YES
+    '';
 
   separateDebugInfo = !stdenv.hostPlatform.isStatic;