### 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 || p_subscript->index == nullptr) {
		return Variant();
	}
	bool is_base_value_reduced = false;
	Variant base_value = make_expression_reduced_value(p_subscript->base, is_base_value_reduced);
	if (!is_base_value_reduced) {
		return Variant();
	}
	if (p_subscript->is_attribute) {
		bool is_valid = false;
		Variant value = base_value.get_named(p_subscript->attribute->name, is_valid);
		if (is_valid) {
			is_reduced = true;
			return value;
		} else {
			return Variant();
		}
	} else {
		bool is_index_value_reduced = false;
		Variant index_value = make_expression_reduced_value(p_subscript->index, is_index_value_reduced);
		if (!is_index_value_reduced) {
			return Variant();
		}