Let $\mathcal{M}_{g,n}$ be the moduli stack over $\mathbb{Q}$ of smooth curves of genus $g$ with $n$ marked points. I've seen in many sources an exact sequence:

$$1\rightarrow\pi_1((\mathcal{M}_{g,n})_{\overline{\mathbb{Q}}})\rightarrow\pi_1(\mathcal{M}_{g,n})\rightarrow\text{Gal}(\overline{\mathbb{Q}}/\mathbb{Q})\rightarrow 1$$

Can someone point to a book/paper where this sequence is proven to be exact?