Added missing modal_closed signal

[qarmin]

Fixes error

 In Object of type 'PopupPanel': Attempt to connect nonexistent signal 'modal_closed' to callable 'ColorPickerButton::_modal_closed'.

[akien-mga]

That's the wrong fix, nothing emits modal closed:

$ rg '"modal_closed"'
scene/gui/color_picker.cpp
997:            popup->connect("modal_closed", callable_mp(this, &ColorPickerButton::_modal_closed));

[qarmin]

Maybe here should be placed emit_signal(based on comment)

godot/editor/editor_spin_slider.cpp

Lines 377 to 381 in 058a0af

	//modal_closed signal
	void EditorSpinSlider::_value_input_closed() {
	_evaluate_input_text();
	value_input_just_closed = true;
	}

[akien-mga]

I'm pretty sure modal_closed was removed on purpose by @reduz since there are no more modal dialogs but everything is Window.

That comment means that this used to be the callback for the modal_closed signal, not its emitter.

[qarmin]

Closing since I have no idea how to fix it.