Change 'self' to 'cls' in mmap.__new__ method (#15576)

Author: jonathandung

stdlib/mmap.pyi

@@ -34,7 +34,7 @@ PAGESIZE: Final[int]
 @disjoint_base
 class mmap:
     if sys.platform == "win32":
-        def __new__(self, fileno: int, length: int, tagname: str | None = None, access: int = 0, offset: int = 0) -> Self: ...
+        def __new__(cls, fileno: int, length: int, tagname: str | None = None, access: int = 0, offset: int = 0) -> Self: ...
     else:
         if sys.version_info >= (3, 13):
             def __new__(