### Godot version

Beta 17, master

### System information

Windows 11

### Issue description

Godot gets a hard crash while attempting to code-complete for member `const` of a class.

### Steps to reproduce

```GDScript
enum E { V1 }

const e := E
```

And then type a `.` after the last `E`, which triggers code hints/auto-completion for subscripts based on `E` and causes a hard crash.

Does not happen for `var e := E.V1`.

### Minimal reproduction project

See above.
case GDScriptParser::IdentifierNode::LOCAL_CONSTANT:
		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::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;