[v1.7.1] can't test error when using mockPrompt

[shadowgate15]

Currently if you do the following:

test('invalid name', async (t) => {
  await t.throwsAsync(
    sao.mock({ generator }, { ...defaults, name: 'Foo Bar Baz Beep' }),
    { message: /package name cannot have uppercase letters/ }
  );
});

the return will be:

Error {
    message: 'validation failed for prompt: [object Object]',
  }

instead of returning the correct error. It does work correctly when not using mock.