Thanks Ilya Khaprov for the fix.

This is the same as `check`. The files of the cross-platform-actions VM
are synchronised in both ways, so we can re-use the same configuration.

`vmactions` VM fails to boot quite frequently and we have no visibility
on the reason of the failure.

The only failure I got out-of-the-box with cross-platform-actions VM was
the `core-deps-rel` test case which hangs. It comes from the use of
`erl_call` to detect if the Erlang node was started correctly. A comment
in the generated release starts scripts says:

    # users who depend on stdout when running rpc calls must still use nodetool
    # so we have an overload option to force use of nodetool instead of erl_call

If `$USE_NODETOOL` is set, it will use `relx_nodetool` instead. Indeed,
this fixed the hang.

It looks like the VM is sometimes stuck booting, long before executing
any tests. The default timeout of 6 hours blocks other CI jobs for a
very long time. Because the VM won't boot anyway, we reduce this time to
one hour.

One hour should be long enough for a successful slow execution of the
tests.

Tests are executed in a FreeBSD VM using the latest stable release. The
default version of Erlang and Elixir from the Ports tree are being used;
currently Erlang/OTP 26 and Elixir 1.17 as of this commit.

Otherwise, tests are split the same way as for Linux/Windows/OSX. That
said, the list is duplicated, so a bit annoying to maintain.

Using the "latest" version doesn't work because it fails to determine
a version for Erlang/OTP.

To work around this, we pin the version of Elixir to "1.18.4-otp-27".

While here, update asdf to version 1.18.0.

With the parallel execution of tests, I think it's possible that an
Erlang VM starts to initialize the missing cookie while a parallel VM
reads an yet-to-be-populated empty file. This leads to the following
crash:

    Slogan: Kernel pid terminated (application_controller) ("{application_start_failure,kernel,{{shutdown,{failed_to_start_child,net_sup,{shutdown,{failed_to_start_child,auth,{\"Too short cookie string\",[{auth,init_no_setcookie,0,[{file,\"auth.erl\"},{line,360}]},...

This commit also includes a way to completely disable Eunit
as that is generally desirable for Elixir-only projects.