CI: optimize packaging tests

Close #541 (closed).

daemon/packaging/centos/7/pre-run.sh

+# SPDX-License-Identifier: GPL-3.0-or-later
+
 yum update -y
-yum install -y https://secure.nic.cz/files/knot-resolver/knot-resolver-release.el.rpm
-yum install -y knot-resolver
+yum install -y wget epel-release
+
+# add build repository
+cd /etc/yum.repos.d/
+wget https://download.opensuse.org/repositories/home:CZ-NIC:knot-resolver-latest/CentOS_7_EPEL/home:CZ-NIC:knot-resolver-latest.repo