test: regenerate lumen golden on linux for CI parity

The lumen preset's temporal accent-mode render exercises the heaviest OKLch
float path (srgb_to_oklch -> mix -> oklch_to_srgb with cbrt/powf/atan2). One
cell in the seed-42 frame lands on a libm rounding boundary where macOS
(arm64) and Linux (x86_64) diverge by 1 ULP, flipping a u8 channel and thus
the golden bytes. CI runs on Linux, so the golden is pinned to Linux output
(regenerated in a rust:latest container). The other three showcase goldens
and temporal_color_accent are byte-identical across both platforms.

Author: tamirelazar