### 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)

#include "spin_box.h"
#include "core/input/input.h"
#include "core/math/expression.h"
Size2 SpinBox::get_minimum_size() const {
	Size2 ms = line_edit->get_combined_minimum_size();
	ms.width += last_w;
	return ms;
}
void SpinBox::_update_text() {
	String value = String::num(get_value(), Math::range_step_decimals(get_step()));
	if (is_localizing_numeral_system()) {
		value = TS->format_number(value);
	}
	if (!line_edit->has_focus()) {
		if (!prefix.is_empty()) {
			value = prefix + " " + value;
		}
		if (!suffix.is_empty()) {
			value += " " + suffix;
		}
	}
	line_edit->set_text_with_selection(value);
}
void SpinBox::_text_submitted(const String &p_string) {