chore: update docs/dyn/index.md

Author: yoshi-automation

docs/dyn/index.md

@@ -482,6 +482,7 @@
 * [v1](http://googleapis.github.io/google-api-python-client/docs/dyn/displayvideo_v1.html)
 * [v2](http://googleapis.github.io/google-api-python-client/docs/dyn/displayvideo_v2.html)
 * [v3](http://googleapis.github.io/google-api-python-client/docs/dyn/displayvideo_v3.html)
+* [v4](http://googleapis.github.io/google-api-python-client/docs/dyn/displayvideo_v4.html)
 
 
 ## dlp