[3.13] Replace ambiguous word "pound" by "hash" in difflib docs (GH-139601) (#139617)

Replace ambiguous word "pound" by "hash" in `difflib` docs (GH-139601)
(cherry picked from commit dadbb26)

Co-authored-by: George Ogden <38294960+George-Ogden@users.noreply.github.com>

Author: miss-islington

Doc/library/difflib.rst

@@ -231,7 +231,7 @@ diffs. For comparing directories and files, see also, the :mod:`filecmp` module.
    *linejunk*: A function that accepts a single string argument, and returns
    true if the string is junk, or false if not. The default is ``None``. There
    is also a module-level function :func:`IS_LINE_JUNK`, which filters out lines
-   without visible characters, except for at most one pound character (``'#'``)
+   without visible characters, except for at most one hash character (``'#'``)
    -- however the underlying :class:`SequenceMatcher` class does a dynamic
    analysis of which lines are so frequent as to constitute noise, and this
    usually works better than using this function.