### 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)

}
						base = look_class->get_datatype();
						found = true;
						break;
					}
					if (look_class->has_member(name)) {
						resolve_class_member(look_class, name, id);
						GDScriptParser::ClassNode::Member member = look_class->get_member(name);
						GDScriptParser::DataType member_datatype = member.get_datatype();
						switch (member.type) {
							case GDScriptParser::ClassNode::Member::CLASS:
								break; 
							case GDScriptParser::ClassNode::Member::CONSTANT:
								if (member_datatype.kind != GDScriptParser::DataType::SCRIPT && member_datatype.kind != GDScriptParser::DataType::CLASS) {
									push_error(vformat(R"(Constant "%s" is not a preloaded script or class.)", name), id);
									return ERR_PARSE_ERROR;
								}
								break;
							default:
								push_error(vformat(R"(Cannot use %s "%s" in extends chain.)", member.get_type_name(), name), id);
								return ERR_PARSE_ERROR;
						}
						base = member_datatype;
						found = true;
						break;
					}
				}
				if (!found) {
					push_error(vformat(R"(Could not find base class "%s".)", name), id);
					return ERR_PARSE_ERROR;