change step size of animation length EditSpinSlider to match minimum animation length
change step size of animation length EditSpinSlider to match minimum animation length

(cherry picked from commit caab6603d187aaa1bd7e70d4fba5aace28642e0a)

ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot