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...

Start by reproducing the `private-access` diagnostics with the GDScript example in the issue, then trace the linter rule that handles private variables and methods. Verify how static context within the same class is classified. Done means the example produces no `private-access` diagnostics while accesses from outside the class remain checked.

Scritto dal modello di indicizzazione a partire dal testo della issue.