### 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::ARRAY:
							case Variant::STRING:
								error = index_type.builtin_type != Variant::INT && index_type.builtin_type != Variant::FLOAT;
								break;
							
							case Variant::RECT2:
							case Variant::RECT2I:
							case Variant::PLANE:
							case Variant::QUATERNION:
							case Variant::AABB:
							case Variant::OBJECT:
								error = index_type.builtin_type != Variant::STRING && index_type.builtin_type != Variant::STRING_NAME;
								break;
							
							case Variant::BASIS:
							case Variant::VECTOR2:
							case Variant::VECTOR2I:
							case Variant::VECTOR3:
							case Variant::VECTOR3I:
							case Variant::VECTOR4:
							case Variant::VECTOR4I:
							case Variant::TRANSFORM2D:
							case Variant::TRANSFORM3D:
							case Variant::PROJECTION:
								error = index_type.builtin_type != Variant::INT && index_type.builtin_type != Variant::FLOAT &&
										index_type.builtin_type != Variant::STRING && index_type.builtin_type != Variant::STRING_NAME;
								break;
							
							case Variant::COLOR:
								error = index_type.builtin_type != Variant::INT && index_type.builtin_type != Variant::STRING && index_type.builtin_type != Variant::STRING_NAME;