Forest styles which include <pgf/tikz key>={<key-value list>} passed to \forest@unknownto without outer braces

[cfr42]

The following code produces a node with a black border, whereas one would intuitively expect a red one.

\documentclass[margin=5pt]{standalone}
\usepackage{forest}
\forestset{%
  egstyle/.style={%
    postaction={draw=red},
  },
}
\begin{document}
\begin{forest}
  [A, egstyle]
\end{forest}
\end{document}

TeX SE question: https://tex.stackexchange.com/questions/703654/alternating-color-borders-of-nodes-and-forest-package/703656?noredirect=1#comment1750649_703656

At least in this case, the problem can be avoided by patching a single line in forest.sty, but I have no idea whether this is safe in general.

forest-patch.txt