Work around msysgit 1.9.4 CliGit test failure in push tags

A Windows Home Server 2011 machine with msysgit 1.9.4 installed on
the D drive fails the push_tags test when the first tag push is
attempted.

The same test has no issue on other Windows machines (Windows 7
and Windows 8.1), and has no issue on the Windows Home Server 2011
machine running JGit.

Rather than deep dive trying to understand why that specific
configuration is behaving unexpectedly for a push of a tag, apply
a work around in the test configuration to configure the branch
from which the repo was cloned.

The work around is a reasonable match for many git plugin use cases.