[bug-fix] Empty ignored trajectory queues, make sure queues don't overflow (#3451)

com.unity.ml-agents/CHANGELOG.md

  - A tutorial on adding custom SideChannels was added (#3391)
  - Update Barracuda to 0.6.0-preview
 
-### Bugfixes
+### Bug Fixes
 - Fixed an issue which caused self-play training sessions to consume a lot of memory. (#3451)
 - Fixed an IndexError when using GAIL or behavioral cloning with demonstrations recorded with 0.14.0 or later (#3464)