iotests: Change imports for Python 3.13

Python 3.13 isn't out yet, but it's in beta and Fedora is ramping up to
make it the default system interpreter for Fedora 41.

They moved our cheese for where ContextManager lives; add a conditional
to locate it while we support both pre-3.9 and 3.13+.

Signed-off-by: John Snow <jsnow@redhat.com>
Message-id: 20240626232230.408004-4-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>
2 files changed