[SSSD] [sssd PR#796][comment] ci: enable sssd-ci for 1-16 branch

[pbrezina]

URL: https://github.com/SSSD/sssd/pull/796
Title: #796: ci: enable sssd-ci for 1-16 branch

pbrezina commented:
"""
It is on purpose. The reason is in the pull request description: Fedora 28 is the latest version that contains SSSD 1.16.  Fedora 29+ contains SSSD 2.0, thus I do not think it is necessary to run 1.16 test on those distros. But if you think it is meaningful, it is easy to add it here as well.
"""

See the full comment at https://github.com/SSSD/sssd/pull/796#issuecomment-479853165