CI tests on macOS

As a follow up of #10794 (closed) it would be nice to add CI tests running on macOS.

I can go grab a Mac Mini later today, but not sure how to hook it up to the CI.

changed milestone to %backlog

Today discussed this on IRC since OpenWRT relies on APK and there are some developers working on macOS; OpenWRT would like to offload testing apk-tools on macOS to upstream.

Options:

• gentle ping for @ariadne if the offer for macOS runner is still available
• Scaleway can possibly sponsor a macOS runner but apparently the experience in managing that is not great
• could possibly try joining MacStadium Open Source waitlist and see if they sponsor a runner (https://www.macstadium.com/company/opensource)

cc: @aparcar @ncopa @clandmeter @Ikke

The MacOS runner was set up (but currently offline, @ariadne?) https://gitlab.alpinelinux.org/admin/runners/232#/

I think you can just create an MR with CI pipe line now and the MacOS runner will pick it up when its back.

mentioned in merge request !276 (merged)