Do not install pixi if it exists when building locally

[hadim]

Comment:

When using pixi as the install tool, it is always installed when building a feedstock locally. See the related code at

conda-smithy/conda_smithy/templates/run_osx_build.sh.tmpl

Line 39 in 2b18d8d

curl -fsSL https://pixi.sh/install.sh | bash

It's less problematic on linux since the build is executed in a container, but it's not the case when building from an osx machine.

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As a side note, I noticed that issue because the feedstock were installing the osx-64 version of pixi (https://github.com/prefix-dev/pixi/releases/latest/download/pixi-x86_64-apple-darwin.tar.gz) instead of the osx-arm64 version. That might also be a bug (if someone with a local osx-arm64 machine could confirm).