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

Bug: webrtc:12338
Change-Id: I85bff694dd2ead83c939c4d1945eff82e1296001
No-Presubmit: True
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/227161
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34690}
diff --git a/modules/audio_processing/audio_processing_impl.cc b/modules/audio_processing/audio_processing_impl.cc
index 4a19855..5acf693 100644
--- a/modules/audio_processing/audio_processing_impl.cc
+++ b/modules/audio_processing/audio_processing_impl.cc
@@ -1325,7 +1325,7 @@
           capture_.key_pressed);
     }
 
-    // Experimental APM sub-module that analyzes |capture_buffer|.
+    // Experimental APM sub-module that analyzes `capture_buffer`.
     if (submodules_.capture_analyzer) {
       submodules_.capture_analyzer->Analyze(capture_buffer);
     }