How to change bullet style to numbers in Metropolis theme

Question

\documentclass{beamer}

\usetheme[progressbar=frametitle]{metropolis}
\usepackage{appendixnumberbeamer}

\begin{document}

\begin{frame}[fragile]{Backup slides}
    Text \cite{Knuth92}
\end{frame}

\begin{frame}[allowframebreaks]{References}
  \bibliography{demo}
  \bibliographystyle{abbrv}
\end{frame}

\end{document}