### Godot version

v4.0.rc1.official [8843d9ad3]

### System information

Lubuntu

### Issue description

You can't use + or += to mutate typed arrays.

It seems to be not correctly getting the type information from the second operand.

An erudite poster on the discord puts it differently:
> it's more like operator + doesn't retain Array typing
> the syntax for Array Concatenation via operators, but the idea gets across i think


The error you see is:
```Trying to assign an array of type "Array" to a variable of type "Array[int]".```


### Steps to reproduce

```
	var Alice: Array[int] = [1,2,3]
	var Bob: Array[int] = [4,5,6]
	Alice += Bob
```
This will crash with the above error message.

### Minimal reproduction project

[plus_syntax_broken_demo_project.zip](https://github.com/godotengine/godot/files/10694514/plus_syntax_broken_demo_project.zip)

}
		ERR_FAIL_COND_V_MSG(!parser_ref->get_parser()->has_class(p_class), ERR_PARSE_ERROR, R"(Parser bug: Mismatched external parser.)");
		GDScriptAnalyzer *other_analyzer = parser_ref->get_analyzer();
		GDScriptParser *other_parser = parser_ref->get_parser();
		int error_count = other_parser->errors.size();
		other_analyzer->resolve_class_inheritance(p_class);
		if (other_parser->errors.size() > error_count) {
			push_error(vformat(R"(Could not resolve inheritance for class "%s".)", p_class->fqcn), p_source);
			return ERR_PARSE_ERROR;
		}
		return OK;
	}
	GDScriptParser::ClassNode *previous_class = parser->current_class;
	parser->current_class = p_class;
	if (p_class->identifier) {
		StringName class_name = p_class->identifier->name;
		if (GDScriptParser::get_builtin_type(class_name) < Variant::VARIANT_MAX) {
			push_error(vformat(R"(Class "%s" hides a built-in type.)", class_name), p_class->identifier);
		} else if (class_exists(class_name)) {
			push_error(vformat(R"(Class "%s" hides a native class.)", class_name), p_class->identifier);
		} else if (ScriptServer::is_global_class(class_name) && (ScriptServer::get_global_class_path(class_name) != parser->script_path || p_class != parser->head)) {
			push_error(vformat(R"(Class "%s" hides a global script class.)", class_name), p_class->identifier);
		} else if (ProjectSettings::get_singleton()->has_autoload(class_name) && ProjectSettings::get_singleton()->get_autoload(class_name).is_singleton) {
			push_error(vformat(R"(Class "%s" hides an autoload singleton.)", class_name), p_class->identifier);
		}
	}
	GDScriptParser::DataType resolving_datatype;
	resolving_datatype.kind = GDScriptParser::DataType::RESOLVING;
	p_class->base_type = resolving_datatype;