gh-96192: fix os.ismount() to use a path that is str or bytes (GH-96194)

(cherry picked from commit 367f552129341796d75fc4cc40edb49405235a2b)

Co-authored-by: Christoph Anton Mitterer <calestyo@scientia.org>
Signed-off-by: Christoph Anton Mitterer <mail@christoph.anton.mitterer.name>
Co-authored-by: Eryk Sun <eryksun@gmail.com>
Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>