[exec.run.loop.types] Add \libconcept for receiver_of (cplusplus#7184)

Author: hewillk

source/exec.tex

@@ -5046,7 +5046,7 @@
 \pnum
 Let \exposid{sndr} be an expression of type \exposid{run-loop-sender},
 let \exposid{rcvr} be an expression
-such that \tcode{receiver_of<decltype((\exposid{rcvr})), CS>} is \tcode{true}
+such that \tcode{\libconcept{receiver_of}<decltype((\exposid{rcvr})), CS>} is \tcode{true}
 where \tcode{CS} is the \tcode{completion_signatures} specialization above.
 Let \tcode{C} be either \tcode{set_value_t} or \tcode{set_stopped_t}.
 Then: