Fix `Test M1` workflow

By passing `--pre` option to `pip install`, otherwise torchvision were always tested against last PyTorch release

.github/workflows/test-m1.yml

@@ -30,7 +30,7 @@ jobs:
           export PATH=~/miniconda3/bin:$PATH
           set -ex
           conda create -yp ${ENV_NAME} python=${PY_VERS} numpy libpng jpeg scipy
-          conda run -p ${ENV_NAME} python3 -mpip install torch --extra-index-url=https://download.pytorch.org/whl/nightly
+          conda run -p ${ENV_NAME} python3 -mpip install --pre torch --extra-index-url=https://download.pytorch.org/whl/nightly
           conda run -p ${ENV_NAME} python3 setup.py develop
           conda run -p ${ENV_NAME} python3 -mpip install pytest pytest-mock av
       - name: Run tests