Mark first argument of __[get|set|del]attr__ as str (#9245)

stubs/openpyxl/openpyxl/styles/named_styles.pyi

@@ -27,7 +27,7 @@ class NamedStyle(Serialisable):  # type: ignore[misc]
         hidden: bool = ...,
         xfId: Any | None = ...,
     ) -> None: ...
-    def __setattr__(self, attr, value) -> None: ...
+    def __setattr__(self, attr: str, value) -> None: ...
     def __iter__(self): ...
     @property
     def xfId(self): ...

stubs/openpyxl/openpyxl/styles/proxy.pyi

@@ -1,7 +1,7 @@
 class StyleProxy:
     def __init__(self, target) -> None: ...
-    def __getattr__(self, attr): ...
-    def __setattr__(self, attr, value) -> None: ...
+    def __getattr__(self, attr: str): ...
+    def __setattr__(self, attr: str, value) -> None: ...
     def __copy__(self): ...
     def __add__(self, other): ...
     def copy(self, **kw): ...