Restore use of cache mounts

[electrofelix]

Adjust syntax used for cache mounts to align with a format supported
by both buildah and docker.

[coveralls]

Pull Request Test Coverage Report for Build 4774368844

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.2%) to 77.409%

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Totals
Change from base Build 4773022767:	0.2%
Covered Lines:	2964
Relevant Lines:	3829

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💛 - Coveralls

[electrofelix]

This will need buildah 1.26 available in the runner.

[github-actions]

Download the latest artifacts for this pull request here:

• vagrant-libvirt-0.11.3.pre.43.gem.zip

[electrofelix]

@dcermak it looks like the version of buildah on the Ubuntu runners work with the mount cache. When I tested this before with https://github.com/vagrant-libvirt/vagrant-libvirt/actions/runs/3147154713/jobs/5116377272 I got the impression that the buildah version wasn't quite new enough and thought 1.26 would be required.

However looking through the history of https://github.com/actions/runner-images/blob/main/images/linux/Ubuntu2204-Readme.md I'm not seeing any indication that buildah was changed in the mean time, nor when I put up a test workflow did it appear that the version had moved on from 1.23.1.

Since it's a bit unclear why it started to work before a new minor release, wondering if you could check this PR change locally to make sure I'm not re-introducing something that will break for other distros where buildah is in use? I've checked it locally and I'm still seeing the same error as before and I'm running 22.04 myself, so I'm a bit wary now of what buildah is actually in the runners.

[electrofelix]

@dcermak never mind, I just spotted my mistake, forgot to update buildah to use the correct ref given I've moved the workflow to use pull_request_target.

[dcermak]

@dcermak never mind, I just spotted my mistake, forgot to update buildah to use the correct ref given I've moved the workflow to use pull_request_target.

Ok, I got confused 😅 because it builds fine with buildah 1.27 on my machine.

[github-actions]

A docker image containing the code from this plugin to allow testing locally without installing
can be pulled from: ghcr.io/vagrant-libvirt/vagrant-libvirt:pr-1613-slim

If you need the image with the full dev toolchain, you can instead pull: ghcr.io/vagrant-libvirt/vagrant-libvirt:pr-1613