Adding validation check to ensure that we are able to build sdist from
the latest tag.
This will allow us to detect sooner when we will try to add a tag to a branch
which is older than another tag already on that branch/in that branch's history
Indeed we recently experienced similar issue [1] with os-collect-config and
tripleo-ipsec where projects hadn't been branched for ussuri [2] and where
we tried to create a new ussuri release [3] on the same hash that an
existing wallaby tag.
Projects have been branched [3] after tags creation [2].
[1] http://lists.openstack.org/pipermail/openstack-discuss/2021-January/020112.html
[2] 688914aa29
[3] ihttps://review.opendev.org/c/openstack/releases/+/772047
Change-Id: Ie2d055f171418e2d35db697dfb1aa17cd449bea9
80652b5232