ci: prepare: Fix Unknown argument error on dnf5

dnf5 does not recognize the `--` argument to mean "end of arguments"
like DNF 4 did.  To terminate the argument list, we need to use the "and
nothing" shell syntax.

ci/prepare.sh

@@ -11,7 +11,7 @@ dnf install -y \
     selinux-policy-devel \
 	tar \
     xz \
-	--
+	&& :
 
 install -m u=rwx,go= -d "${GNUPGHOME}"
 cat > "${GNUPGHOME}"/gpg-agent.conf <<EOF