specs: avoid tickling sc_error_message_uppercase sanity check.

* specs/spec_helper.lua.in (raise): An alias to the error matcher
to subvert matching `error` followed by `"[A-Z]` that prevents
make dist from completing.
* specs/container_spec.yaml (construction): Use the raise alias.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>