fixup: fix return[s] spelling and use codeblock to avoid overfull hbox

Co-authored-by: Jan Schultke <[email protected]>

Author: dietmarkuehl

source/exec.tex

@@ -6425,8 +6425,10 @@
 \begin{itemdescr}
 \pnum
 \effects
-Equivalent to: \tcode{returns await_transform(just(exchange(SCHED(*this),
-\linebreak scheduler_type(sch.scheduler))), *this);} % avoid Overfull
+Equivalent to:
+\begin{codeblock}
+return await_transform(just(exchange(SCHED(*this),  scheduler_type(sch.scheduler))), *this);
+\end{codeblock}
 \end{itemdescr}
 
 \begin{itemdecl}