`setup-libmagic-version` GitHub Action

[robo9k]

The repo already contains an Action to setup libmagic on Linux, macOS, Windows - but the version cannot be specified

There's a test workflow against all supported versions that does most of the needed tasks on the Ubuntu runners already and could be extracted from:

• install dependencies
• download release tarball
• check shasum
• untar, autoreconf
• configure
• make, make install
• provide env vars for pkg-config
• provide version feature for crate

This could be used in the rust-magic repo as well, which needs latest API but not all features

Other users might want to configure more than --enable-static, e.g. xz deps

Other thoughts:

• could use tags from file/file repo instead of release tarballs
• might be able to cache installed prefix dir