$(css, el) does not work in light dom

[sashafirsov]

instead, it returns empty chain

const el = await fixture<LightDomElement>(
            html`<light-dom-element>
                    <template>
                        <button>action</button>
                    </template>
                </light-dom-element>`
        );
        expect($('button', el).txt()).to.equal('action');