Biblatex citations inside KOMA-script's dictum

Question

I would like to use biblatex (specifically, biblatex-chicago) to cite an author inside the \dictum command of scrbook.

Here's my MWE, which produces some errors.

\documentclass{scrbook}

\usepackage{lipsum}
\usepackage[authordate,backend=biber]{biblatex-chicago}
\addbibresource{test.bib}

\begin{filecontents*}{test.bib}
@book{Marshall1920,
    title={Principles of Economics},
    subtitle={An Introductory Volume},
    author={Marshall, Alfred},
    publisher={Macmillan and Co.},
    location={London},
    edition={8},
    date={1920}}
\end{filecontents*}

\begin{document}
\renewcommand*{\dictumauthorformat}[1]{#1}
    \setchapterpreamble[u]{\dictum[\textcite[][782]{Marshall1920}]{If we shut our eyes to realities we may construct an edifice of pure crystal by imaginations, that will grow side lights on real problems; and might conceivably be of interest to beings who had no economic problems like our own.}}
\chapter{A chapter heading}
\lipsum[1]

\printbibliography
\end{document}

It also produces a missing font related warning, but I thought I would not modify the font for the sake of keeping the example as minimal as possible.

I would rather continue using \dictum rather than switching to package epigraph or something similar, if this is possible.