Test a unusual rebar3 corner case where an Elixir package, built with mix plugin, is released.
If done directly, without previous build, the release will fail.
Repeat the release, or compile/test before the first release, and the release is successful.

First build rebar3 escript used by this test suite.
 rebar3 escriptize

This is a bandaid, covering that this one time vsn is a binary,
instead of a list. One real solution would be to find out why vsn
is binary, and change it there.