Fix a couple of comments.

These were discovered while reviewing Aleksander Alekseev's
proposed changes to pgindent.

Oversights in commits 393e0d2314 and 25a30bbd42.

Discussion: https://postgr.es/m/aP-H6kSsGOxaB21k%40nathan

src/backend/storage/ipc/waiteventset.c

@@ -2010,7 +2010,7 @@ ResOwnerReleaseWaitEventSet(Datum res)
  * NB: be sure to save and restore errno around it.  (That's standard practice
  * in most signal handlers, of course, but we used to omit it in handlers that
  * only set a flag.) XXX
-  *
+ *
  * NB: this function is called from critical sections and signal handlers so
  * throwing an error is not a good idea.
  *