Update tests workflow badge in README

Replace the tests badge URL in README.md to point to the new GitHub Actions workflow (test_and_deploy.yml) and include branch=main in the badge URL so the status reflects the correct workflow/branch.

Author: C-Achard

README.md

@@ -9,7 +9,7 @@
 [![License: LGPL-3.0](https://img.shields.io/badge/License-LGPL%203.0-blue.svg)](https://www.gnu.org/licenses/lgpl-3.0)
 [![PyPI](https://img.shields.io/pypi/v/napari-deeplabcut.svg?color=green)](https://pypi.org/project/napari-deeplabcut)
 [![Python Version](https://img.shields.io/pypi/pyversions/napari-deeplabcut.svg?color=green)](https://python.org)
-[![tests](https://github.com/DeepLabCut/napari-deeplabcut/workflows/tests/badge.svg)](https://github.com/DeepLabCut/napari-deeplabcut/actions)
+[![tests](https://github.com/DeepLabCut/napari-deeplabcut/actions/workflows/test_and_deploy.yml/badge.svg?branch=main)](https://github.com/DeepLabCut/napari-deeplabcut/actions/workflows/test_and_deploy.yml)
 [![codecov](https://codecov.io/gh/DeepLabCut/napari-deeplabcut/branch/main/graph/badge.svg)](https://codecov.io/gh/DeepLabCut/napari-deeplabcut)
 [![napari hub](https://img.shields.io/endpoint?url=https://api.napari-hub.org/shields/napari-deeplabcut)](https://napari-hub.org/plugins/napari-deeplabcut)