Fix venv activation: source activate script instead of env var

Signed-off-by: Pablo Garay <[email protected]>

Author: pablo-garay

.github/workflows/generate-lockfile.yml

@@ -57,7 +57,7 @@ jobs:
 
               # Create venv with system packages (this makes container torch available)
               uv venv /opt/venv --system-site-packages
-              export UV_PROJECT_ENVIRONMENT=/opt/venv
+              source /opt/venv/bin/activate
 
               # Pre-install build dependencies before any sync/lock operation
               uv pip install setuptools wheel pybind11 "Cython>=3.0.0" "numpy<2.0.0" ninja packaging poetry