### 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)

if (p_subscript->base == nullptr) {
		return;
	}
	if (p_subscript->base->type == GDScriptParser::Node::IDENTIFIER) {
		reduce_identifier(static_cast<GDScriptParser::IdentifierNode *>(p_subscript->base), true);
	} else if (p_subscript->base->type == GDScriptParser::Node::SUBSCRIPT) {
		reduce_subscript(static_cast<GDScriptParser::SubscriptNode *>(p_subscript->base), true);
	} else {
		reduce_expression(p_subscript->base);
	}
	GDScriptParser::DataType result_type;
	if (p_subscript->is_attribute) {
		if (p_subscript->attribute == nullptr) {
			return;
		}
		GDScriptParser::DataType base_type = p_subscript->base->get_datatype();
		bool valid = false;
		
		if (p_subscript->base->is_constant && !base_type.is_meta_type) {
			
			Variant value = p_subscript->base->reduced_value.get_named(p_subscript->attribute->name, valid);