requirements: no pygithub 1.54 due to conflict
requirements: no pygithub 1.54 due to conflict

PyGithub package conflicts with current latest
version of requirements due to bug in different pkg (httpretty) [1].

Since that was fixed, pygithub already reverted their pinning [2],
so new version they release it should be ok, but 1.54 is not, so lets
avoid that one.

[1] https://github.com/PyGithub/PyGithub/commit/d159425f36dc7f68766cc980e262e9287e5f111c
[2] https://github.com/PyGithub/PyGithub/pull/1763

RHOSINFRA-3792

Change-Id: Ica59289ece01b48dd19d098b1881f3b784ecd533

redhat-openstack/infrared,redhat-openstack/infrared,redhat-openstack/infrared