p11-kit: add darwin tls ca store path

[lilyinstarlight]

Description of changes

Allows p11-kit to correctly find the root CA store on macOS. This is relevant when building something like curl with NSS and are intending to use libnssckbi (p11-trust-kit) for the CA store (like the curl-impersonate-ff derivation from #194310)

I tested this in GitHub Actions (since I don't have a Mac) and this patch allowed curl-impersonate-ff to work correctly

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 22.11 Release Notes (or backporting 22.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
  • (Release notes changes) Ran nixos/doc/manual/md-to-db.sh to update generated release notes
• Fits CONTRIBUTING.md.

[lilyinstarlight]

@rnhmjoj, any chance this could be merged before the next staging cycle starts or do you want someone else to give it an additional review first?

[rnhmjoj]

I was giving some time for others to review, but it been a while and this change should be completely harmless.
Let's merge this.