### 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 (info.path.get_extension().to_lower() != GDScriptLanguage::get_singleton()->get_extension()) {
					push_error(vformat(R"(Singleton %s is not a GDScript.)", info.name), id);
					return ERR_PARSE_ERROR;
				}
				Ref<GDScriptParserRef> info_parser = get_parser_for(info.path);
				if (info_parser.is_null()) {
					push_error(vformat(R"(Could not parse singleton from "%s".)", info.path), id);
					return ERR_PARSE_ERROR;
				}
				Error err = info_parser->raise_status(GDScriptParserRef::INHERITANCE_SOLVED);
				if (err != OK) {
					push_error(vformat(R"(Could not resolve super class inheritance from "%s".)", name), id);
					return err;
				}
				base = info_parser->get_parser()->head->get_datatype();
			} else if (class_exists(name)) {
				base.kind = GDScriptParser::DataType::NATIVE;
				base.native_type = name;
			} else {
				
				bool found = false;
				List<GDScriptParser::ClassNode *> script_classes;
				get_class_node_current_scope_classes(p_class, &script_classes);
				for (GDScriptParser::ClassNode *look_class : script_classes) {
					if (look_class->identifier && look_class->identifier->name == name) {
						if (!look_class->get_datatype().is_set()) {
							Error err = resolve_class_inheritance(look_class, id);
							if (err) {
								return err;
							}