Update ruby-magic to v0.6.0

What does this MR do and why?

This gives us the ability to disable newly added zstd decompression support for in libmagic with the --with-magic-flags option (https://github.com/kwilczynski/ruby-magic/pull/39).

This will be used with omnibus-gitlab!6749 (merged).

Relates to omnibus-gitlab#7672 (closed)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.