Update CHANGELOG-EE.md for 13.9.4-ee

[ci skip]

CHANGELOG-EE.md

 Please view this file on the master branch, on stable branches it's out of date.
+## 13.9.4 (2021-03-17)
+
+- No changes.
+
 ## 13.9.3 (2021-03-08)
 - No changes.