pixi run start says "command not found" but it's only the platform that's missing

[wolfv]

Checks

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

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

Reproducible example

[project]
name = "test"
version = "0.1.0"
description = "Add a short description here"
authors = []
channels = ["conda-forge"]
platforms = ["linux-64"]

[tasks]
start = "echo hello"

Now execute on a platform that is not linux-64 (e.g. osx-arm64)

pixi run start

Issue description

This prints:

start: command not found

It would be better if it prints "osx-arm64 not supported" or not in platforms or something like that.

Expected behavior

Print a more helpful error message.