[execution.syn] Fix comment alignment

Author: Andreas-Krug

source/exec.tex

@@ -565,7 +565,7 @@
     using @\exposidnc{single-sender-value-type}@ = @\seebelownc@;                 // \expos
 
   template<class Sndr, class... Env>
-    concept @\exposconcept{single-sender}@ = @\seebelow@; // \expos
+    concept @\exposconcept{single-sender}@ = @\seebelow@;                         // \expos
 
   template<@\libconcept{sender}@ Sndr>
     using tag_of_t = @\seebelow@;