### 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)

p_type->set_datatype(result);
		return result;
	}
	StringName first = p_type->type_chain[0]->name;
	if (first == SNAME("Variant")) {
		if (p_type->type_chain.size() == 2) {
			
			StringName enum_name = p_type->type_chain[1]->name;
			StringName qualified_name = String(first) + ENUM_SEPARATOR + String(p_type->type_chain[1]->name);
			if (CoreConstants::is_global_enum(qualified_name)) {
				result = make_global_enum_type(enum_name, first, true);
				return result;
			} else {
				push_error(vformat(R"(Name "%s" is not a nested type of "Variant".)", enum_name), p_type->type_chain[1]);
				return bad_type;
			}
		} else if (p_type->type_chain.size() > 2) {
			push_error(R"(Variant only contains enum types, which do not have nested types.)", p_type->type_chain[2]);
			return bad_type;
		}
		result.kind = GDScriptParser::DataType::VARIANT;
	} else if (first == SNAME("Object")) {
		
		result.kind = GDScriptParser::DataType::NATIVE;
		result.builtin_type = Variant::OBJECT;
		result.native_type = SNAME("Object");
	} else if (GDScriptParser::get_builtin_type(first) < Variant::VARIANT_MAX) {
		
		if (p_type->type_chain.size() > 1) {
			push_error(R"(Built-in types don't contain nested types.)", p_type->type_chain[1]);