Verify that VERSION_ID matches ALPINE_VERSION in the new ISO

[jandubois]

Looks like some part of the build is not pinned down, making the builds non-reproducible.

[jandubois]

The build always uses the latest Alpine base for the ISO; the ALPINE_VERSION setting just specifies the tag that we checkout for the aports submodule (and therefore determines the version of the mkimage.sh script).

This can be confusing because the VERSION_ID from /etc/os-release may not match the Alpine version in the ISO filename.

I don't know if it is possible to build from an older base (and think it is kind of pointless, except for reproducibility), but we should at least make sure the filename (and aports version) match the actual Alpine version in the ISO.

[jandubois]

For example the https://github.com/lima-vm/alpine-lima/releases/tag/v0.2.47 assets claim to be Alpine 3.23.0 but are actually 3.23.2.