### 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)

}
		}
	} else if (!p_is_lambda && function_name == GDScriptLanguage::get_singleton()->strings._static_init) {
		
		GDScriptParser::DataType return_type;
		return_type.kind = GDScriptParser::DataType::BUILTIN;
		return_type.builtin_type = Variant::NIL;
		p_function->set_datatype(return_type);
		if (p_function->return_type) {
			GDScriptParser::DataType declared_return = resolve_datatype(p_function->return_type);
			if (declared_return.kind != GDScriptParser::DataType::BUILTIN || declared_return.builtin_type != Variant::NIL) {
				push_error("Static constructor cannot have an explicit return type.", p_function->return_type);
			}
		}
	} else {
		if (p_function->return_type != nullptr) {
			p_function->set_datatype(type_from_metatype(resolve_datatype(p_function->return_type)));
		} else {
			
			
			GDScriptParser::DataType return_type;
			return_type.type_source = GDScriptParser::DataType::INFERRED;
			return_type.kind = GDScriptParser::DataType::VARIANT;
			p_function->set_datatype(return_type);
		}
#ifdef TOOLS_ENABLED
		
		
		GDScriptParser::DataType base_type = parser->current_class->base_type;
		base_type.is_meta_type = false;