[exec.task.scheduler] Fix punctuation and add 'the'

Fixes NB US 241-371 (C++26 CD).

Author: jensmaurer

source/exec.tex

@@ -7085,8 +7085,8 @@
 \begin{itemdescr}
 \pnum
 \returns
-\tcode{false} if type of \tcode{\exposid{SCHED}(lhs)} is not \tcode{Sch},
-otherwise \tcode{\exposid{SCHED}(lhs) == rhs;}
+\tcode{false} if the type of \tcode{\exposid{SCHED}(lhs)} is not \tcode{Sch},
+otherwise \tcode{\exposid{SCHED}(lhs) == rhs}.
 \end{itemdescr}
 
 \pnum