Tests: python: path-like object introduced in python 3.6

Tests: python: path-like object introduced in python 3.6

Prior to python 3.6 the builtin open() function expected a string or
bytes object for the pathname. Add a compat method to convert the
path-like object to a string on interpreters that lack PEP-519 [1]
support.

[1] https://peps.python.org/pep-0519/

Change-Id: I23d1da1202e17db621f1fb89f7a79b12694dd4a6
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>