main/py3-markdown: upgrade to 3.4.1

3.3.6...3.4.1

af38c427 Disallow square brackets in reference link ids.
383de86c [style]: fix various typos in docstrings and comments
f6ca7542 Fix typos and remove trailing spaces
ed417a1a extensions: copy config dict on each highlighted block
ce73b275 Ensure fenced code attributes are properly escaped.
21ba00c2 Add markdown-link-check github action.
db98a263 Bump version to 3.3.7
659a4365 Update th/td to use style attribute
0f5f8af0 fixed link #1154
efec51ac Footnotes improvements
93d17b9c Support custom CSS class on TOC element
9d90d471 Support for custom Pygments formatter
0394b26c Use @deprecated for Registry.add()
7334ecd4 Use @deprecated for setitem and delitem of Registry.
12c3378a Pass language to Pygments formatter in CodeHilite
e958ec41 Only enumerate extension entry points when required
cebe1de2 Drop support for PY36
96d27f19 Add None check to PrettifyTreeprocessor
dc434df7 Update PrettifyTreeprocessor <pre><code> handling
a767b2da Remove previously deprecated objects
97359a4a Remove redundant lines from PrettifyTreeprocessor
77fb7f1b fixed some spelling mistakes
c0f6e5a3 Move backslash unescaping to treeprocessor
a884a991 Bump version to 3.4
3c581264 Fix import issue with importlib.util
f588d8b0 Bump version to 3.4.1