### 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::UNDEFINED_SOURCE:
			break;
	}
	
	if (!found_source) {
		reduce_identifier_from_base(p_identifier);
		if (p_identifier->source != GDScriptParser::IdentifierNode::UNDEFINED_SOURCE || p_identifier->get_datatype().is_set()) {
			
			found_source = true;
		}
	}
	if (found_source) {
		bool source_is_variable = p_identifier->source == GDScriptParser::IdentifierNode::MEMBER_VARIABLE || p_identifier->source == GDScriptParser::IdentifierNode::INHERITED_VARIABLE;
		bool source_is_signal = p_identifier->source == GDScriptParser::IdentifierNode::MEMBER_SIGNAL;
		if ((source_is_variable || source_is_signal) && static_context) {
			if (parser->current_function) {
				
				GDScriptParser::FunctionNode *parent_function = parser->current_function;
				while (parent_function->source_lambda) {
					parent_function = parent_function->source_lambda->parent_function;
				}
				push_error(vformat(R"*(Cannot access %s "%s" from the static function "%s()".)*", source_is_signal ? "signal" : "instance variable", p_identifier->name, parent_function->identifier->name), p_identifier);
			} else {
				push_error(vformat(R"*(Cannot access %s "%s" for a static variable initializer.)*", source_is_signal ? "signal" : "instance variable", p_identifier->name), p_identifier);
			}
		}
		if (!lambda_stack.is_empty()) {
			
			if (source_is_variable || source_is_signal) {
				mark_lambda_use_self();