Update escape sequences for compatibility with python3.12.

(Closes: #1068853)

These particular escapes were previously listed as DeprecationWarning,
but in Python 3.12 were changed to a SyntaxWarming:

  https://discuss.python.org/t/collaboration-on-handling-python-3-12-incompatible-changes-distutils-and-asyncore-removal-invalid-escape-escape-etc/20721

Used the recommended pycodestyle command to find the specific issues:

  pycodestyle --show-source --select W605 $(find -name "*.py")

Wow, this is getting ugly!