### Godot version

4.1.1

### System information

linux

### Issue description

The `"%+f"` format adds a `+` sign in front of positive numbers. If you try to format `-0.0`, it breaks and displays both a `+` and a `-`.

### Steps to reproduce

```gdscript
@tool
extends EditorScript

func _run() -> void:
    print("%+f" % -0.0)
```

### Minimal reproduction project

see above
TEST_CASE("[String] Variant validated indexed get") {
	Variant s = String("abcd");
	Variant::ValidatedIndexedGetter getter = Variant::get_member_validated_indexed_getter(Variant::STRING);
	Variant r;
	bool oob = true;
	getter(&s, 1, &r, &oob);
	CHECK_FALSE(oob);
	CHECK_EQ(r, String("b"));
}
TEST_CASE("[String] Variant ptr indexed get") {
	String s("abcd");
	Variant::PTRIndexedGetter getter = Variant::get_member_ptr_indexed_getter(Variant::STRING);
	String r;
	getter(&s, 1, &r);
	CHECK_EQ(r, String("b"));
}
TEST_CASE("[String] Variant indexed set") {
	Variant s = String("abcd");
	bool valid = false;
	bool oob = true;
	s.set_indexed(1, String("z"), valid, oob);
	CHECK(valid);
	CHECK_FALSE(oob);
	CHECK_EQ(s, String("azcd"));
}
TEST_CASE("[String] Variant validated indexed set") {
	Variant s = String("abcd");
	Variant::ValidatedIndexedSetter setter = Variant::get_member_validated_indexed_setter(Variant::STRING);
	Variant v = String("z");
	bool oob = true;