### 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)

reduce_expression(p_assignment->assignee);
	reduce_expression(p_assignment->assigned_value);
	if (p_assignment->assigned_value == nullptr || p_assignment->assignee == nullptr) {
		return;
	}
	GDScriptParser::DataType assignee_type = p_assignment->assignee->get_datatype();
	if (assignee_type.is_constant) {
		push_error("Cannot assign a new value to a constant.", p_assignment->assignee);
		return;
	} else if (p_assignment->assignee->type == GDScriptParser::Node::SUBSCRIPT && static_cast<GDScriptParser::SubscriptNode *>(p_assignment->assignee)->base->is_constant) {
		const GDScriptParser::DataType &base_type = static_cast<GDScriptParser::SubscriptNode *>(p_assignment->assignee)->base->datatype;