Use backticks not vertical bars to denote variables in comments for /rtc_base

Bug: webrtc:12338
Change-Id: I72fcb505a92f03b2ace7160ee33d555a977eddfd
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/226955
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34587}

rtc_base/task_queue_libevent.cc

@@ -281,7 +281,7 @@ void TaskQueueLibevent::OnWakeup(int socket,
         if (task->Run()) {
           task.reset();
         } else {
-          // |false| means the task should *not* be deleted.
+          // `false` means the task should *not* be deleted.
           task.release();
         }
       }