Harness::render creates a wgpu device on its first call, and egui_kittest
prefers a CPU adapter. When cargo test runs several of these tests on
parallel threads, the deckcraft-ui-egui test binary can exit with
0xc0000005 (STATUS_ACCESS_VIOLATION), so cargo xtask ci stops at its test
step on Windows without cargo-nextest.
The 16 tests that call render now hold one mutex for their whole run
(crate::gpu_lock::gpu_lock, as in photocraft's testkit), so only one of
them runs at a time.