Add debug statement

.github/workflows/source_distribution_tests.yml

@@ -94,6 +94,8 @@ jobs:
       - name: Test that module is importable
         run: python -v -c 'from google._upb import _message; assert "google._upb._message.MessageMeta" in str(_message.MessageMeta)'
         if: ${{ !matrix.pure_python }}
+      - name: [Debug] Print installs
+        run: pip list -v
       - name: Run the unit tests
         run: |
           TESTS=$(pip show -f protobuftests | grep pb_unit_tests.*py$ | sed 's,/,.,g' | sed 's,\\,.,g' | sed -E 's,.py$,,g')