[futures.async] Add missing space to fold expression

Author: JohelEGP

source/threads.tex

@@ -7224,7 +7224,7 @@
 The following are all \tcode{true}:
 \begin{itemize}
 \item \tcode{is_constructible_v<decay_t<F>, F>},
-\item \tcode{(is_constructible_v<decay_t<Args>, Args> \&\&...)}, and
+\item \tcode{(is_constructible_v<decay_t<Args>, Args> \&\& ...)}, and
 \item \tcode{is_invocable_v<decay_t<F>, decay_t<Args>...>}.
 \end{itemize}