pixi does not respect channel and mirrors settings

[ianzone]

Checks

• [X] I have checked that this issue has not already been reported.

• [X] I have confirmed this bug exists on the latest version of pixi, using pixi --version.

Reproducible example

~/.pixi/config.toml

detached-environments = false

[mirrors]
"https://conda.anaconda.org/" = ["https://mirrors.tuna.tsinghua.edu.cn/anaconda/cloud/"]
"https://conda.anaconda.org/nvidia" = ["https://mirrors.sustech.edu.cn/anaconda-extra/cloud/nvidia/"]

[repodata-config]
disable-jlap = true
disable-zstd = true

pixi.toml

[project]
channels = ["nvidia", "conda-forge", "pytorch"]
name = "d2l"
platforms = ["linux-64"]
version = "0.1.0"

[dependencies]
cuda = { channel = "nvidia" }

❯ pixi search cuda
 
Using channels: nvidia, conda-forge, pytorch

cuda ha804496_0
---------------

Name                cuda
Version             12.6.1
Build               ha804496_0
Size                26689
License             LicenseRef-NVIDIA-End-User-License-Agreement
Subdir              noarch
File Name           cuda-12.6.1-ha804496_0.conda
URL                 https://conda.anaconda.org/conda-forge/noarch/cuda-12.6.1-ha804496_0.conda
MD5                 79c7f0280c94d5b9707fd1fcf4832738
SHA256              11bc3c354b01be0b10d0a354ec91e6e847e8af2f798bbe6eaced12c07235f4c6

Dependencies:
 - __linux
 - cuda-runtime 12.6.1.*
 - cuda-toolkit 12.6.1.*

Issue description

the cuda info is fetched from neither nvidia channel nor the mirrors.tuna.tsinghua.edu.cn

Expected behavior

the URL should be like https://mirrors.sustech.edu.cn/anaconda-extra/cloud/nvidia/cuda-12.6.1-ha804496_0.conda