Fix bash syntax

Author: asmeurer

.github/workflows/tests.yml

@@ -33,9 +33,9 @@ jobs:
       - name: Run Tests
         run: |
           if [ "${{ matrix.numpy-version }}" == "1.21" ]; then
-             PYTEST_EXTRA="-k 'numpy and not jax'"
+             PYTEST_EXTRA=(-k "numpy and not jax")
           fi
-          pytest $PYTEST_EXTRA
+          pytest "${PYTEST_EXTRA[@]}"
 
           # Make sure it installs
           python setup.py install