ci: prepare: Fix syntax for dnf5 in Fedora 41

Apparently, `dnf5` differs from `dnf` in that it does not ignore the
trailing `--` argument:

> Unknown argument "--" for command "install". Add "--help" for more
> information about the arguments.

ci/prepare.sh

@@ -13,7 +13,7 @@ dnf install -y \
 	rust \
 	systemd-rpm-macros \
 	tar \
-	--
+	&& :
 
 install -m u=rwx,go= -d "${GNUPGHOME}"
 cat > "${GNUPGHOME}"/gpg-agent.conf <<EOF