### Godot version

v4.0.3.stable.official [5222a99f5]
Master [6101240231600c871f5c5473872532c68ea3268c] (confirmed by https://github.com/godotengine/godot/issues/77666#issuecomment-1568952502)

### System information

Window 10

### Issue description

References are not unreferenced at the end of `if` scopes.

### Steps to reproduce

Copy, paste and run the snippet below, check the results:

```gdscript
extends Node


func _ready() -> void:
  var ref := RefCounted.new()
  var ref_count : int

  # OK
  ref_count = ref.get_reference_count()
  print('Expected: 1, Result: %d' % ref_count)

  # OK
  if true:
    var temp := ref
    temp = null

  ref_count = ref.get_reference_count()
  print('Expected: 1, Result: %d' % ref_count)

  # FAIL
  if true:
    var temp := ref

  ref_count = ref.get_reference_count()
  print('Expected: 1, Result: %d' % ref_count)
```

Output example:

```
Expected: 1, Result: 1
Expected: 1, Result: 1
Expected: 1, Result: 2
```

### Minimal reproduction project

N/A
IdentifierNode *id = static_cast<IdentifierNode *>(p_previous_operand);
			switch (id->source) {
				case IdentifierNode::LOCAL_VARIABLE:
					source_variable = id->variable_source;
					id->variable_source->usages--;
					break;
				case IdentifierNode::LOCAL_CONSTANT:
					id->constant_source->usages--;
					break;
				case IdentifierNode::FUNCTION_PARAMETER:
					id->parameter_source->usages--;
					break;
				case IdentifierNode::LOCAL_ITERATOR:
				case IdentifierNode::LOCAL_BIND:
					id->bind_source->usages--;
					break;
				default:
					break;
			}
#endif
		} break;
		case Node::SUBSCRIPT:
			
			break;
		default:
			push_error(R"(Only identifier, attribute access, and subscription access can be used as assignment target.)");
			return parse_expression(false); 
	}
	AssignmentNode *assignment = alloc_node<AssignmentNode>();
	reset_extents(assignment, p_previous_operand);