The knockback of stun machine is broken

Summary

Entity is disable to be knockback when it is stunning.

Steps to reproduce

Mob:

TEST2:
 Type: zombie
 Skills:
 - stun{d=200;nokb=false} @self ~onSpawn

Current behavior

Entity doesn't get knockback when it got hit.

Intended correct behavior

When stunning entity got hit, it will be knockback.

Server log file

No errors.

Debug log snippet

No errors.

Proposed fixes

None.