### 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 (!valid) {
				push_error(vformat(R"(Cannot get index "%s" from "%s".)", p_subscript->index->reduced_value, p_subscript->base->reduced_value), p_subscript->index);
				result_type.kind = GDScriptParser::DataType::VARIANT;
			} else {
				p_subscript->is_constant = true;
				p_subscript->reduced_value = value;
				result_type = type_from_variant(value, p_subscript);
			}
		} else {
			GDScriptParser::DataType base_type = p_subscript->base->get_datatype();
			GDScriptParser::DataType index_type = p_subscript->index->get_datatype();
			if (base_type.is_variant()) {
				result_type.kind = GDScriptParser::DataType::VARIANT;
				mark_node_unsafe(p_subscript);
			} else {
				if (base_type.kind == GDScriptParser::DataType::BUILTIN && !index_type.is_variant()) {
					
					bool error = index_type.kind != GDScriptParser::DataType::BUILTIN && base_type.builtin_type != Variant::DICTIONARY;
					if (!error) {
						switch (base_type.builtin_type) {
							
							case Variant::PACKED_BYTE_ARRAY:
							case Variant::PACKED_COLOR_ARRAY:
							case Variant::PACKED_FLOAT32_ARRAY:
							case Variant::PACKED_FLOAT64_ARRAY:
							case Variant::PACKED_INT32_ARRAY:
							case Variant::PACKED_INT64_ARRAY:
							case Variant::PACKED_STRING_ARRAY:
							case Variant::PACKED_VECTOR2_ARRAY:
							case Variant::PACKED_VECTOR3_ARRAY: