add pythonpath for running python scenes

Author: fredroy

.github/workflows/ci.yml

@@ -139,6 +139,7 @@ jobs:
             # Setup mandatory env vars
             export REGRESSION_SCENES_DIR="${WORKSPACE_SRC_PATH}/examples"
             export REGRESSION_REFERENCES_DIR="${WORKSPACE_SRC_PATH}/regression/references"
+            export PYTHONPATH=$SOFA_ROOT/plugins/SofaPython3/lib/python3/site-packages
             # Run regression test bench
             ${SOFA_ROOT}/bin/Regression_test${{ steps.sofa.outputs.exe }}
           else