[3.13] gh-85045: clarified that the underlying buffer of a TextIOBase can be a RawIOBase (GH-134372) (#134375)

gh-85045: clarified that the underlying buffer of a TextIOBase can be a RawIOBase (GH-134372)

Added a clarification that the underlying binary buffer of a TextIOBase can be a BufferedIOBase OR a RawIOBase
(cherry picked from commit 36eb711d2f26849214774a017fe8c8a5be3eec30)

Co-authored-by: Alex Kautz <alex@takemobi.com>