ci-buildpackage: Avoid git-restore as it is too new

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>

package-source-builder/overlay/usr/bin/ci-buildpackage

@@ -20,7 +20,7 @@ apt-get -qy -o APT::Get::Build-Dep-Automatic=yes \
   build-dep "$(pwd)"
 
 # Revert changes made by `wrap-and-sort`
-git restore debian
+git checkout debian/
 
 dpkg-checkbuilddeps