Linter: "private-access" incorrectly triggers on access from static context within same class

## Description

The rule `private-access` is triggered when accessing a private instance member from a static context within the same class. See the example below.

The rule message is "... should not be accessed *from outside its class*" which let me think this is not intentional and is a bug.

## Reproduce

```gdscript
class_name Foo

var _data: int

func _method() -> void:
pass

static func do(foo: Foo) -> void:
foo._data = 0
foo._method()
```

## Expected behaviour

No linter rule triggered.

## Observed behaviour

The above example triggers :
`[private-access] Private variable '_data' should not be accessed from outside its class`
`[private-access] Private method '_method' should not be accessed from outside its class`

But this is not an access from outside the class...

まず、issue にある GDScript の例で `private-access` 診断を再現し、次にプライベート変数とメソッドを処理する linter ルールを追跡します。同じクラス内の静的コンテキストがどのように分類されるかを確認します。例で `private-access` 診断が生成されず、クラス外からのアクセスについては引き続きチェックされれば完了です。

索引モデルが issue の本文から書いたものです。