Use of `git restore` has been introduced in commit e954d2be
"ci-buildpackage: use wrap-and-sort as a workaround for odd packages".

It works on the Bullseye-based v2022dev2, but on older Buster-based
release `git restore` is not available.

Replace it with the old-style `git checkout`.

Signed-off-by: Emanuele Aina <emanuele.aina@collabora.com>