This should fix our CI, which is currently failing on any system which
requires using the zlib subproject (typically VS systems) as wrapdb is
down. Work around that by pointing our wrap file at the underlying
github hosting instead.
See https://github.com/mesonbuild/meson/issues/6446#issuecomment-574241715
This can be reverted when wrapdb is working again.
Signed-off-by: Philip Withnall <withnall@endlessm.com>