### Tested versions

- Reproducible in: v4.2.stable.arch_linux
- Not Reproducible in: v4.1.3.stable.official [f06b6836a]

### System information

Garuda Linux (2.6.19-2)

### Issue description

A minor issue where UI Icons are not rendering on the Group Editor window, attaching a screenshot for reference:
![Screenshot_604](https://github.com/godotengine/godot/assets/22623256/c366164a-3d9a-4dcf-97a0-199b5a5a7ecc)

The icons were expected for Buttons like Add, Remove, Filter, etc.

### Steps to reproduce

Select any Node and go to the `Node` panel, click `Manage Groups` and the window will open.

### Minimal reproduction project (MRP)

Minor issue, easily reproducible following the above steps.
add_filter = memnew(LineEdit);
	add_filter->set_h_size_flags(Control::SIZE_EXPAND_FILL);
	add_filter->set_placeholder(TTR("Filter Nodes"));
	add_filter_hbc->add_child(add_filter);
	add_filter->connect("text_changed", callable_mp(this, &GroupDialog::_add_filter_changed));
	VBoxContainer *vbc_buttons = memnew(VBoxContainer);
	hbc->add_child(vbc_buttons);
	vbc_buttons->set_h_size_flags(Control::SIZE_SHRINK_CENTER);
	vbc_buttons->set_v_size_flags(Control::SIZE_SHRINK_CENTER);
	add_button = memnew(Button);
	add_button->set_flat(true);
	add_button->set_text(TTR("Add"));
	add_button->connect("pressed", callable_mp(this, &GroupDialog::_add_pressed));
	vbc_buttons->add_child(add_button);
	vbc_buttons->add_spacer();
	vbc_buttons->add_spacer();
	vbc_buttons->add_spacer();
	remove_button = memnew(Button);
	remove_button->set_flat(true);
	remove_button->set_text(TTR("Remove"));
	remove_button->connect("pressed", callable_mp(this, &GroupDialog::_removed_pressed));
	vbc_buttons->add_child(remove_button);
	VBoxContainer *vbc_remove = memnew(VBoxContainer);
	hbc->add_child(vbc_remove);
	vbc_remove->set_h_size_flags(Control::SIZE_EXPAND_FILL);
	Label *in_group_title = memnew(Label);
	in_group_title->set_theme_type_variation("HeaderSmall");
	in_group_title->set_text(TTR("Nodes in Group"));
	vbc_remove->add_child(in_group_title);
	nodes_to_remove = memnew(Tree);