[Fix] Fix PyTorch installation in merge stage test (#1158)

fix merge stage test

.github/workflows/merge_stage_test.yml

@@ -139,7 +139,7 @@ jobs:
         run: |
           apt-get update && apt-get install -y ffmpeg libsm6 libxext6 git ninja-build libglib2.0-0 libsm6 libxrender-dev libxext6
       - name: Install PyTorch
-        run: pip install torch==1.8.1+cpu torchvision==0.9.1+cpu -f https://download.pytorch.org/whl/lts/1.8/torch_lts.html
+        run: python -m pip install torch==1.8.1+cpu torchvision==0.9.1+cpu -f https://download.pytorch.org/whl/lts/1.8/torch_lts.html
       - name: Install mmediting dependencies
         run: |
           pip install git+https://github.com/open-mmlab/mmengine.git@main