README: adjust for final Azure Pipeline ID

During the six months of development of the Azure Pipelines support, the patches went through quite a few iterations of changes, and to test those iterations, a temporary build definition was used. In the meantime, Azure Pipelines support made it to `master`, and we now have a regular Azure Pipeline, installed via the common GitHub App workflow. This new pipeline has a different name (git.git instead of test-git.git), and a new ID (11 instead of 2). Let's adjust the badge in our README to reflect that final shape of the Azure Pipeline. Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>