Doc: Update py2app link. (#91585)

See: https://mail.python.org/archives/list/docs@python.org/thread/KDVFGNGGUGGPVRZT7WZYHHWXCRS2GEN7/

Doc/using/mac.rst

@@ -160,7 +160,7 @@ Distributing Python Applications on the Mac
 
 The standard tool for deploying standalone Python applications on the Mac is
 :program:`py2app`. More information on installing and using py2app can be found
-at http://undefined.org/python/#py2app.
+at https://pypi.org/project/py2app/.
 
 
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