### 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)

case Variant::VECTOR3:
					case Variant::VECTOR4:
					case Variant::QUATERNION:
						result_type.builtin_type = Variant::FLOAT;
						break;
					
					case Variant::PACKED_COLOR_ARRAY:
						result_type.builtin_type = Variant::COLOR;
						break;
					
					case Variant::PACKED_STRING_ARRAY:
					case Variant::STRING:
						result_type.builtin_type = Variant::STRING;
						break;
					
					case Variant::PACKED_VECTOR2_ARRAY:
					case Variant::TRANSFORM2D:
					case Variant::RECT2:
						result_type.builtin_type = Variant::VECTOR2;
						break;
					
					case Variant::RECT2I:
						result_type.builtin_type = Variant::VECTOR2I;
						break;
					
					case Variant::PACKED_VECTOR3_ARRAY:
					case Variant::AABB:
					case Variant::BASIS:
						result_type.builtin_type = Variant::VECTOR3;
						break;