### 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)

case GDScriptParser::IdentifierNode::MEMBER_CONSTANT:
			p_identifier->set_datatype(p_identifier->constant_source->get_datatype());
			p_identifier->is_constant = true;
			
			p_identifier->reduced_value = p_identifier->constant_source->initializer->reduced_value;
			found_source = true;
			break;
		case GDScriptParser::IdentifierNode::MEMBER_SIGNAL:
		case GDScriptParser::IdentifierNode::INHERITED_VARIABLE:
			mark_lambda_use_self();
			break;
		case GDScriptParser::IdentifierNode::MEMBER_VARIABLE:
			mark_lambda_use_self();
			p_identifier->variable_source->usages++;
			[[fallthrough]];
		case GDScriptParser::IdentifierNode::STATIC_VARIABLE:
		case GDScriptParser::IdentifierNode::LOCAL_VARIABLE:
			p_identifier->set_datatype(p_identifier->variable_source->get_datatype());
			found_source = true;
			break;
		case GDScriptParser::IdentifierNode::LOCAL_ITERATOR:
			p_identifier->set_datatype(p_identifier->bind_source->get_datatype());
			found_source = true;
			break;
		case GDScriptParser::IdentifierNode::LOCAL_BIND: {
			GDScriptParser::DataType result = p_identifier->bind_source->get_datatype();
			result.is_constant = true;
			p_identifier->set_datatype(result);
			found_source = true;
		} break;