When more than one stable-queue branch is provided, the first series is
downloaded as `series` and the next is downloaded as `series.1`. The
series for the subsequent branches must overwrite the patch series of
the previous branch or we end up using the patch series for the first
branch for all branches.

This patch ensures that the `series` file is always overwritten for
additional branches included in stable-queue.

Signed-off-by: Major Hayden <major@redhat.com>