Use Pixi in macOS-intel CI

[scott-huberty]

I'm exploring the feasibility of using Pixi to resolve the virtual environment and run tests specifically for the MacOS Intel CI, which currently uses Mamba to create the virtual environment.

My initial strategy was to just to do pixi init --import environment.yml, so that we can leverage our already defined YAML config file to pull in all the necessary dependencies, as well as configuring prefix-dev/setup-pixi to automatically activate our virtual environment, so that we can run commands like pytest etc without having to prepend pixi run everywhere for the pixi CI...

Unfortunately the only way I could get this to work was to disable use of a login shell.. Which of course makes all the condo-like CI's fail!!

[tsbinns]

Hey @scott-huberty, looking at the current diff I noticed you're setting up pixi without activating the env, initing with environment.yml, then setting up again with env activation.

Found when switching to uv for the old job that the env can be activated at setup with a given Python ver and then have the required packages installed in github_actions_dependencies.sh:

mne-python/.github/workflows/tests.yml

Lines 157 to 165 in 8dd298f

	- uses: astral-sh/setup-uv@v7
	with:
	version: ">=0.9"
	activate-environment: true
	cache-dependency-glob: |
	**/pylock.ci-old.toml
	python-version: ${{ matrix.python }}
	if: matrix.kind == 'old'
	- run: bash ./tools/github_actions_dependencies.sh

Wondered if a similar thing could work for pixi rather than needing 2 setups. Haven't looked through diffs for all commits, so apologies if you tried this already.