[stoptoken.concepts] Add \tcode for terminate (#7516)

Author: Andreas-Krug

source/threads.tex

@@ -801,7 +801,7 @@
 the stop state's registered callback invocations shall be
 synchronously executed.
 If an invocation of a callback exits via an exception
-then terminate shall be invoked\iref{except.terminate}.
+then \tcode{terminate} shall be invoked\iref{except.terminate}.
 \begin{note}
 No constraint is placed on the order
 in which the callback invocations are executed.