tests: drivers: can: shell: poll for the dummy shell to be ready

static void *can_shell_setup(void)

{

	/* Let the shell backend initialize. */

	k_msleep(20);

	const struct shell *sh = shell_backend_dummy_get_ptr();

	/* Wait for the initialization of the shell dummy backend. */

	WAIT_FOR(shell_ready(sh), 20000, k_msleep(1));

	zassert_true(shell_ready(sh), "timed out waiting for dummy shell backend");

	return NULL;

}