### 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)

#else
				push_error(vformat(R"(Cannot find constant "%s" on base "%s".)", name, base.to_string()), p_identifier);
#endif 
			}
		} else {
			switch (base.builtin_type) {
				case Variant::NIL: {
					if (base.is_hard_type()) {
						push_error(vformat(R"(Invalid get index "%s" on base Nil)", name), p_identifier);
					}
					return;
				}
				case Variant::DICTIONARY: {
					GDScriptParser::DataType dummy;
					dummy.kind = GDScriptParser::DataType::VARIANT;
					p_identifier->set_datatype(dummy);
					return;
				}
				default: {
					Callable::CallError temp;
					Variant dummy;
					Variant::construct(base.builtin_type, dummy, nullptr, 0, temp);
					List<PropertyInfo> properties;
					dummy.get_property_list(&properties);
					for (const PropertyInfo &prop : properties) {
						if (prop.name == name) {
							p_identifier->set_datatype(type_from_property(prop));
							return;
						}
					}