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

Bug: webrtc:12338
Change-Id: I2a33903a79194bb092a17ea1e1505bf2a3377d8b
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/227027
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34558}

test/rtp_file_reader.h

diff --git a/test/rtp_file_reader.h b/test/rtp_file_reader.h
index 1fa6f72..2c39340 100644
--- a/test/rtp_file_reader.h
+++ b/test/rtp_file_reader.h
@@ -22,7 +22,7 @@
   static const size_t kMaxPacketBufferSize = 3500;
   uint8_t data[kMaxPacketBufferSize];
   size_t length;
-  // The length the packet had on wire. Will be different from |length| when
+  // The length the packet had on wire. Will be different from `length` when
   // reading a header-only RTP dump.
   size_t original_length;