third_party/Python-Markdown: Update to 3.4.1

All modifications are from upstream

Change-Id: I463e327b3cf15aeb9cd86da03b3c28c880278e19
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4048800


Auto-Submit: 揚帆起航 <uioptt24@gmail.com>
Commit-Queue: Dirk Pranke <dpranke@google.com>
Reviewed-by: Dirk Pranke <dpranke@google.com>
Cr-Commit-Position: refs/heads/main@{#1076461}