[fix] since git v2.35.2 root can't read from unsafe repository

Git v2.35.2 closes an security issue, it is no longer possible that root uses a
git repo that is owned by someone else, the error message is::

    fatal: unsafe repository ('/share/darmarit.org/cache/searxng' is owned by someone else)

The fix is to run the `git diff --name-only` not as root in a sudo command.

[1] https://github.blog/2022-04-12-git-security-vulnerability-announced/


Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>