Better error message for missing local channel

[nichmor]

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

[project]
name = "resnet"
version = "0.1.0"
description = "Add a short description here"
authors = ["Nichita Morcotilo <[email protected]>"]
channels = ["../local", "conda-forge"]
platforms = ["osx-arm64"]

[dependencies]
pytorch = "*"

Issue description

Having defined a local channel in channels = ["../local", "conda-forge"] will show following error:

Expected behavior

As a user I would like to see more friendly error message indicating what channel pixi can't find