message: Add test that constructs expected<T> from none_t
diff: @@ -112,3 +112,9 @@ CAF_TEST(move_and_copy) {
  CHECK_NEQ(z, z_cpy);
  CHECK_EQ(z, sec::unsupported_sys_key);
  }
  +
  +CAF_TEST(construction_with_none) {
  + e_int x{none};
  + CHECK(!x);
  + CHECK(!x.error());
  +}
  