Add some 7zip zstd reader tests

Add some 7zip zstd reader tests

There is a popular 7-Zip fork with zstandard support, with releases as
far back as 2017:
https://github.com/mcmilk/7-Zip-zstd.git

Zstandard support is not yet available in 7-Zip, though it is planned
for a future release:
https://sourceforge.net/p/sevenzip/feature-requests/1580/

This change adds a couple of tests for reading 7-Zip archives which
use zstandard compression. They are expected to fail until support is
added in the following commit.

Relates to #1656.