### Godot version

v4.0.beta13.official [caacade56]

### System information

Linux Ubuntu 20.04 with Unity desktop

### Issue description

When calling an undefined function in the shader editor with argument(s), such as `undefined_function(1)`, the error reads:

> Too many arguments for "undefined_function()" call. Expected at most 0 but received 1.

instead of the expected:

> No matching function found for: 'undefined_function'.

This is possibly a regression introduced in https://github.com/godotengine/godot/issues/18225, since the latter was focused on the arguments part.

To avoid such regression in the future, consider adding a unit test with this case (and, in fact, unit tests for the other signature errors too if there are not already).

### Steps to reproduce

1. Create a shader resource and open the shader editor
2. Enter `undefined_function(1);` in the fragment() definition

### Minimal reproduction project

N/A
switch (p_op) {
		case OP_ASSIGN:
		case OP_ASSIGN_ADD:
		case OP_ASSIGN_SUB:
		case OP_ASSIGN_MUL:
		case OP_ASSIGN_DIV:
		case OP_ASSIGN_MOD:
		case OP_ASSIGN_SHIFT_LEFT:
		case OP_ASSIGN_SHIFT_RIGHT:
		case OP_ASSIGN_BIT_AND:
		case OP_ASSIGN_BIT_OR:
		case OP_ASSIGN_BIT_XOR:
			return true;
		default:
			return false;
	}
}
bool ShaderLanguage::_validate_varying_assign(ShaderNode::Varying &p_varying, String *r_message) {
	if (current_function != "vertex" && current_function != "fragment") {
		*r_message = vformat(RTR("Varying may not be assigned in the '%s' function."), current_function);
		return false;
	}
	switch (p_varying.stage) {
		case ShaderNode::Varying::STAGE_UNKNOWN: