maintain-github-mirror: add requests dependency
maintain-github-mirror: add requests dependency

maintain-github-mirror makes direct use of the requests module. That
module is currently installed as a dependency of PyGithub, but that's
brittle, as PyGithub may well opt for a different library in the
future.

Let's proactively fix that before it bites us.

Change-Id: I8fc288e6c3978e20ddf48f905968931f89834e53

openstack-infra/project-config,openstack-infra/project-config