gpui: Remove mutex from dynamic font loading (#64204)

Dynamic font loading is useful on web, but locked a mutex on the main
thread. This PR removes that

---

Release Notes:

- N/A or Added/Fixed/Improved ...
b68add5b37Cameron Mcloughlin committed on 9/14/2026, 11:49:34 PM· committed by GitHubparent9e6e141
2 files changedLine totals unavailable