python3-markdown: upgrade 3.5 -> 3.5.2

python3-markdown: upgrade 3.5 -> 3.5.2

Changelog:
============
-Fix type annotations for convertFile - it accepts only bytes-based buffers.
 Also remove legacy checks from Python 2
-Remove legacy import needed only in Python 2
-Fix typo that left the attribute AdmonitionProcessor.content_indent unset
-Fix edge-case crash in InlineProcessor with AtomicString.
-Fix edge-case crash in codehilite with an empty code tag.
-Improve and expand type annotations in the code base.
-Fix handling of bogus comments

Signed-off-by: Wang Mingyu <wangmy@fujitsu.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>