### Godot version

4.2.dev3.official

### System information

Windows 10 - GLES3 (Compatibility)

### Issue description

When a text is typed into the SpinBox node, and the `Enter` key is pressed, the text is normally removed, and the last valid number value of the SpinBox is restored.
However, when the string that is input is `"Nil"`, pressing `Enter` won't remove it, as it would do with any other text.

https://github.com/godotengine/godot/assets/141344817/a866a597-02db-4195-b45e-87578e0f1f92

### Steps to reproduce

0. Create a new project.
1. Add SpinBox node.
2. Run the project.
3. Input any valid number into the SpinBox.
4. Try to input some text into the SpinBox.
5. Try to type and input "Nil" text into the SpinBox.

### Minimal reproduction project

[SpinBox Nil - MRP.zip](https://github.com/godotengine/godot/files/12453969/SpinBox.Nil.-.MRP.zip)

return update_on_text_changed;
}
void SpinBox::set_select_all_on_focus(bool p_enabled) {
	line_edit->set_select_all_on_focus(p_enabled);
}
bool SpinBox::is_select_all_on_focus() const {
	return line_edit->is_select_all_on_focus();
}
void SpinBox::set_editable(bool p_enabled) {
	line_edit->set_editable(p_enabled);
}
bool SpinBox::is_editable() const {
	return line_edit->is_editable();
}
void SpinBox::apply() {
	_text_submitted(line_edit->get_text());
}
void SpinBox::set_custom_arrow_step(double p_custom_arrow_step) {
	custom_arrow_step = p_custom_arrow_step;
}
double SpinBox::get_custom_arrow_step() const {