Describe the bug
PNG -> JXL lossy conversion changes brightness

To Reproduce

• download this sample
• convert to jxl lossless (the image looks the same)
• convert to jxl quality=96 (the image becomes much darker)

Expected behavior
Image brightness should not change upon png->jxl conversion

Screenshots
Left half source/jxl_lossless, right half - jxl_q96

Environment

• OS: Windows
• CPU type: x86_64
• cjxl/djxl version string: cjxl 0.11.0 4df1e9e [AVX2,SSE2]