Update pypi_test.yaml

.github/workflows/pypi_test.yaml

@@ -40,6 +40,7 @@ jobs:
           sudo apt install libeigen3-dev
           git submodule init
           git submodule update
+          export PIP_CACHE_DIR=dist/
       #     git fetch --tags -f
       #     mkdir build && cd build
       #     cmake .. && make install -j 4 && cd ..