docs: replace "Mac OS X" -> "macOS" (GH-27364)

"Mac OS X" has been rebranded as macOS

https://www.apple.com/macos

Doc/library/os.rst

@@ -194,7 +194,7 @@ process and user.
 
    .. note::
 
-      On some platforms, including FreeBSD and Mac OS X, setting ``environ`` may
+      On some platforms, including FreeBSD and macOS, setting ``environ`` may
       cause memory leaks.  Refer to the system documentation for
       :c:func:`putenv`.
 
@@ -369,7 +369,7 @@ process and user.
 
    .. note::
 
-      On Mac OS X, :func:`getgroups` behavior differs somewhat from
+      On macOS, :func:`getgroups` behavior differs somewhat from
       other Unix platforms. If the Python interpreter was built with a
       deployment target of :const:`10.5` or earlier, :func:`getgroups` returns
       the list of effective group ids associated with the current user process;
@@ -516,7 +516,7 @@ process and user.
 
    .. note::
 
-      On some platforms, including FreeBSD and Mac OS X, setting ``environ`` may
+      On some platforms, including FreeBSD and macOS, setting ``environ`` may
       cause memory leaks. Refer to the system documentation for :c:func:`putenv`.
 
    .. audit-event:: os.putenv key,value os.putenv
@@ -554,7 +554,7 @@ process and user.
 
    .. availability:: Unix.
 
-   .. note:: On Mac OS X, the length of *groups* may not exceed the
+   .. note:: On macOS, the length of *groups* may not exceed the
       system-defined maximum number of effective group ids, typically 16.
       See the documentation for :func:`getgroups` for cases where it may not
       return the same group list set by calling setgroups().
@@ -1379,11 +1379,11 @@ or `the MSDN <https://msdn.microsoft.com/en-us/library/z0kc8e3z.aspx>`_ on Windo
    On Linux, if *offset* is given as ``None``, the bytes are read from the
    current position of *in_fd* and the position of *in_fd* is updated.
 
-   The second case may be used on Mac OS X and FreeBSD where *headers* and
+   The second case may be used on macOS and FreeBSD where *headers* and
    *trailers* are arbitrary sequences of buffers that are written before and
    after the data from *in_fd* is written. It returns the same as the first case.
 
-   On Mac OS X and FreeBSD, a value of ``0`` for *count* specifies to send until
+   On macOS and FreeBSD, a value of ``0`` for *count* specifies to send until
    the end of *in_fd* is reached.
 
    All platforms support sockets as *out_fd* file descriptor, and some platforms