アニメーションに終了メソッド呼び出しを手作業で追加するのが面倒だからスクリプト書いた
4では治っているようだがバックポートはなさそう #70278
tool
extends EditorScript

func _run():
var path = "res://units/player.tscn"
var animation_name = "AttackSord"
var target_node = "/root/SystemNode"
var target_func = "animation_finished"
var scene = load(path).instance(0)
var player = scene.get_node("AnimationPlayer")
var animation = player.get_animation(animation_name)

# find last key time
var t = 0.0
for track_index in animation.get_track_count():
for key_index in animation.track_get_key_count(track_index):
t = max(t, animation.track_get_key_time(track_index, key_index))

# add method key
var index = animation.add_track(Animation.TYPE_METHOD, -1)
animation.track_set_path(index, target_node)
var params = { "method": target_func, "args": [animation_name] }
animation.track_insert_key(index, t, params, 1)

var packer = PackedScene.new()
if packer.pack(scene) == OK:
var e = ResourceSaver.save(path, packer)
if e != OK:
print(e)