Formatting incorrect in ui.markdown with markdown2==2.4.11

[thetableman]

Description

I recently created a new venv and found that the text output of ui.markdown suddenly displayed incorrectly with an exisiting project. It seems when installing NiceGUI from pip the new venv grabbed markdown2==2.4.11 whereas the previous was 2.4.10.

from nicegui import ui

ui.markdown('''Test **Markdown**.  
                **over** multiple lines.''')

ui.run

With markdown2==2.4.10

With markdown2==2.4.11

The issue seems to arise when a new line starts with markdown identifiers.

[falkoschindler]

Thanks for the bug report, @thetableman!
There is an upstream bug trentm/python-markdown2#546 which has already been fixed. Until it gets released, we should indeed apply your PR #2154. 👍