### 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)

return;
	}
	if (GDScriptLanguage::get_singleton()->has_any_global_constant(name)) {
		Variant constant = GDScriptLanguage::get_singleton()->get_any_global_constant(name);
		p_identifier->set_datatype(type_from_variant(constant, p_identifier));
		p_identifier->is_constant = true;
		p_identifier->reduced_value = constant;
		return;
	}
	if (CoreConstants::is_global_enum(name)) {
		p_identifier->set_datatype(make_global_enum_type(name, StringName(), true));
		if (!can_be_builtin) {
			push_error(vformat(R"(Global enum "%s" cannot be used on its own.)", name), p_identifier);
		}
		return;
	}
	
	if (can_be_builtin && name == SNAME("Variant")) {
		GDScriptParser::DataType variant;
		variant.kind = GDScriptParser::DataType::VARIANT;
		variant.type_source = GDScriptParser::DataType::ANNOTATED_EXPLICIT;
		variant.is_meta_type = true;
		variant.is_pseudo_type = true;
		p_identifier->set_datatype(variant);
		return;
	}
	
	
	if (GDScriptUtilityFunctions::function_exists(name)) {
		push_error(vformat(R"(Built-in function "%s" cannot be used as an identifier.)", name), p_identifier);