SyntaxWarning when starting `jupyter nbclassic`

[living180]

When starting jupyter nbclassic under Python 3.12, the first line printed is:

/tmp/venv/lib/python3.12/site-packages/nbclassic/notebookapp.py:327: SyntaxWarning: invalid escape sequence '\/'

This is due to ASCII art which uses backslashes in a literal fashion rather than for escape sequences:

nbclassic/nbclassic/notebookapp.py

Lines 328 to 333 in abe28bc

	print("""
	_ _ _ _
	| | | |_ __ __| |__ _| |_ ___
	| |_| | '_ \/ _` / _` | _/ -_)
	\___/| .__/\__,_\__,_|\__\___|
	|_|

.