fixup! Unified windows build

Author: mshabunin

.github/workflows/OCV-PR-Windows.yaml

@@ -116,7 +116,7 @@ jobs:
       working-directory: '${{ github.workspace }}'
       run: |
         # ls -lR '${{ env.DNN_MODELS }}'
-        python3 opencv_extra/testdata/dnn/download_models.py \
+        python opencv_extra/testdata/dnn/download_models.py \
           --cleanup \
           --dst '${{ env.DNN_MODELS }}/dnn'
         echo "OPENCV_DNN_TEST_DATA_PATH=${{ env.DNN_MODELS }}" >> $GITHUB_ENV