Use updated PrivateKits package

[BomberFish]

This updates the PrivateKits package used in Cowabunga, which also allows it to successfully build on Xcode 15.

TODO:

• [x] Test on real hardware
• [x] Verify no features, especially icon theming, are impacted

[BomberFish]

Everything still works as intended on real hardware, so this PR doesn't break anything!