Use Git_jll

[mattBrzezinski]

Instead of using the command-line git in the tests we should switch to Git_jll as the command-line git may not be installed. The command would look something like:

using Git_jll
git() do git_path
    read(`$git_path ls-remote --tags https://github.com/JuliaLang/julia`, String)
end

Unfortunately there seems to be an issues at the moment:

• https://github.com/JuliaBinaryWrappers/Git_jll.jl/issues/2
• Git_jll: fatal: unable to find remote helper for 'https' JuliaPackaging/Yggdrasil#1299