Make warning arg keyword only

Co-authored-by: M Bussonnier <[email protected]>

Author: steppi

jupyterlite_sphinx/_try_examples.py

@@ -3,7 +3,7 @@
 import re
 
 
-def examples_to_notebook(input_lines, warning_text=None):
+def examples_to_notebook(input_lines, *, warning_text=None):
     """Parse examples section of a docstring and convert to Jupyter notebook.
 
     Parameters