### 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 (base_type.kind != GDScriptParser::DataType::BUILTIN) {
					base_type.builtin_type = Variant::OBJECT;
				}
				switch (base_type.builtin_type) {
					
					case Variant::RID:
					case Variant::BOOL:
					case Variant::CALLABLE:
					case Variant::FLOAT:
					case Variant::INT:
					case Variant::NIL:
					case Variant::NODE_PATH:
					case Variant::SIGNAL:
					case Variant::STRING_NAME:
						result_type.kind = GDScriptParser::DataType::VARIANT;
						push_error(vformat(R"(Cannot use subscript operator on a base of type "%s".)", base_type.to_string()), p_subscript->base);
						break;
					
					case Variant::PACKED_BYTE_ARRAY:
					case Variant::PACKED_INT32_ARRAY:
					case Variant::PACKED_INT64_ARRAY:
					case Variant::VECTOR2I:
					case Variant::VECTOR3I:
					case Variant::VECTOR4I:
						result_type.builtin_type = Variant::INT;
						break;
					
					case Variant::PACKED_FLOAT32_ARRAY:
					case Variant::PACKED_FLOAT64_ARRAY:
					case Variant::VECTOR2: