Correctly forward JxlBasicInfo.alpha_premultiplied #11023

Job	Run time
Release linux x86_64 static	7m 35s
.deb packages / ubuntu:22.04	22m 38s
Windows Build (vcpkg / x64-windows-static)	16m 0s
.deb packages / ubuntu:20.04	14m 2s
.deb packages / ubuntu:24.04	25m 2s
.deb packages / debian:bookworm	13m 28s
.deb packages / debian:bullseye	12m 45s
Windows Build (vcpkg / x86-windows-static)	7m 38s
Windows Build (vcpkg / x64-windows)	6m 39s
Windows Build (vcpkg / x86-windows)	5m 17s
Publish release assets	0s
	2h 11m 4s

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