[ci] Add linux arm64 build

[tobil4sk]

Hxcpp has had support for linux arm for some time, and haxe is already running linux arm hxcpp tests.

For some reason, the cffi test currently fails on arm64 linux:

Called from TestCffi::boot src/TestCffi.hx line 17
Called from cpp.Lib::load cpp/Lib.hx line 38
Error : Could not load module prime@isBool__1

I'll try to emulate locally to figure it out.

[tobil4sk]

The failure is caused by a missing arm64 case in __hxcpp_get_bin_dir(). There is an open pr to fix it: #1355.

[MRK2009]

You mentioned my pr? Noice