### 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)

if (found) {
				break;
			}
			if (script_class->identifier && script_class->identifier->name == first) {
				result = script_class->get_datatype();
				break;
			}
			if (script_class->members_indices.has(first)) {
				resolve_class_member(script_class, first, p_type);
				GDScriptParser::ClassNode::Member member = script_class->get_member(first);
				switch (member.type) {
					case GDScriptParser::ClassNode::Member::CLASS:
						result = member.get_datatype();
						found = true;
						break;
					case GDScriptParser::ClassNode::Member::ENUM:
						result = member.get_datatype();
						found = true;
						break;
					case GDScriptParser::ClassNode::Member::CONSTANT:
						if (member.get_datatype().is_meta_type) {
							result = member.get_datatype();
							found = true;
							break;
						} else if (Ref<Script>(member.constant->initializer->reduced_value).is_valid()) {
							Ref<GDScript> gdscript = member.constant->initializer->reduced_value;
							if (gdscript.is_valid()) {
								Ref<GDScriptParserRef> ref = get_parser_for(gdscript->get_script_path());
								if (ref->raise_status(GDScriptParserRef::INHERITANCE_SOLVED) != OK) {
									push_error(vformat(R"(Could not parse script from "%s".)", gdscript->get_script_path()), p_type);