conda-pypi-map always triggers a warning

[gzm55]

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

cat >pixi.toml <<END
[project]
name = "test"
platforms = ["linux-64"]
version = "0.1"
conda-pypi-map = { "conda-forge" = "https://fake.com" }
channels = ["conda-forge", "https://conda.anaconda.org/conda-forge/" ]
END

pixi update

Issue description

always generate warning

WARN Defined custom mapping channel https://conda.anaconda.org/conda-forge/ is missing from project channels

and do not set any global configurations

Expected behavior

Should not print this warning.

[benglewis]

I also have this same issue. Is there any way to resolve it?

[ruben-arts]

We're working on it in #1820