### 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)

}
						element.resolved = true;
					}
					enum_type.enum_values[element.identifier->name] = element.value;
					dictionary[String(element.identifier->name)] = element.value;
				}
				current_enum = prev_enum;
				dictionary.make_read_only();
				member.m_enum->set_datatype(enum_type);
				member.m_enum->dictionary = dictionary;
				
				for (GDScriptParser::AnnotationNode *&E : member.m_enum->annotations) {
					resolve_annotation(E);
					E->apply(parser, member.m_enum);
				}
			} break;
			case GDScriptParser::ClassNode::Member::FUNCTION:
				for (GDScriptParser::AnnotationNode *&E : member.function->annotations) {
					resolve_annotation(E);
					E->apply(parser, member.function);
				}
				resolve_function_signature(member.function, p_source);
				break;
			case GDScriptParser::ClassNode::Member::ENUM_VALUE: {
				member.enum_value.identifier->set_datatype(resolving_datatype);
				if (member.enum_value.custom_value) {
					check_class_member_name_conflict(p_class, member.enum_value.identifier->name, member.enum_value.custom_value);
					const GDScriptParser::EnumNode *prev_enum = current_enum;
					current_enum = member.enum_value.parent_enum;
					reduce_expression(member.enum_value.custom_value);