microtype is broken with fontspec 2.9b when using \textls with fonts whose names contain spaces

[teoric]

Description

Since upgrading to fontspec v2.9b in current TeXlive, microtype's \textls does not work any more for fonts with spaces(?).

[x] Relevant for LuaTeX

Minimal example demonstrating the issue

\documentclass{article}
\usepackage{unicode-math}

% \setmainfont[Ligatures={TeX}]{Carlito} % works
\setmainfont[Ligatures={TeX}]{Libertinus Serif} % does not work
\usepackage[]{microtype}

\begin{document}

Kaffe\textls{kanne}

\end{document}

Further details

error message:

luaotfload | db : Reload initiated (formats: otf,ttf,ttc); reason: Font "kernfactor=0.1;Libertinus Serif" not found

rolling back to fontspec v2.9a, the spacing works and no error message appears.

This issue was originally reported to fontspec, but @u-fischer thinks it's more microtype's than fontspec's responsibility to fix this.