Update pwd stub file (#5741)

Add the following properties to struct_passwd:
* n_fields
* n_sequence_fields
* n_unnamed_fields

Co-authored-by: Akuli <[email protected]>

Author: LeMeteore

stdlib/pwd.pyi

@@ -1,4 +1,4 @@
-from typing import List, Tuple
+from typing import ClassVar, List, Tuple
 
 class struct_passwd(Tuple[str, str, int, int, str, str, str]):
     pw_name: str
@@ -9,6 +9,10 @@ class struct_passwd(Tuple[str, str, int, int, str, str, str]):
     pw_dir: str
     pw_shell: str
 
+    n_fields: ClassVar[int]
+    n_sequence_fields: ClassVar[int]
+    n_unnamed_fields: ClassVar[int]
+
 def getpwall() -> List[struct_passwd]: ...
 def getpwuid(__uid: int) -> struct_passwd: ...
 def getpwnam(__name: str) -> struct_passwd: ...