import-debian-package: do not use Path objects as a context manager

pathlib.Path.__enter__() is deprecated and scheduled for removal
in Python 3.13. Some warnings are generated with Python 3.11:

import-debian-package:281: DeprecationWarning: pathlib.Path.__enter__() is deprecated and scheduled for removal in Python 3.13; Path objects as a context manager is a no-op
  with Path(".git/info/attributes") as f:
import-debian-package:225: DeprecationWarning: pathlib.Path.__enter__() is deprecated and scheduled for removal in Python 3.13; Path objects as a context manager is a no-op
  with Path('debian/apertis/component') as f:
import-debian-package:169: DeprecationWarning: pathlib.Path.__enter__() is deprecated and scheduled for removal in Python 3.13; Path objects as a context manager is a no-op
  with Path("debian/changelog") as f:

Signed-off-by: Dylan Aïssi <dylan.aissi@collabora.com>