add news entry

Author: akulakov

Misc/NEWS.d/next/Library/2021-07-09-07-14-37.bpo-41928.Q1jMrr.rst

@@ -0,0 +1,4 @@
+Update :func:`shutil.copyfile` to raise :exc:`FileNotFoundError` instead of
+confusing :exc:`IsADirectoryError` when a path ending with a
+:const:`os.path.sep` does not exist; :func:`shutil.copy` and
+:func:`shutil.copy2` are also affected.