fix CIBW_TEST_COMMAND

Author: mattip

.github/workflows/ci.yaml

@@ -511,7 +511,7 @@ jobs:
         CIBW_BUILD: ${{ matrix.spec }}
         CIBW_PRERELEASE_PYTHONS: 'True'
         CIBW_TEST_REQUIRES: pytest setuptools pytest-xdist filelock
-        CIBW_TEST_COMMAND: 'python -m pytest {package}/src/c {project}/testing -n 4'
+        CIBW_TEST_COMMAND: cd {project}; PYTHONUNBUFFERED=1 pytest -n 4
       run: |
         set -eux