More work on numpy version tests.

Author: tshead

.github/workflows/regression-tests.yml

@@ -26,7 +26,7 @@ jobs:
         sudo apt-get install ffmpeg ghostscript
         python -m pip install --upgrade pip
         pip install coveralls
-        pip install ${{ matrix.numpy-version }}
+        pip install "${{ matrix.numpy-version }}"
         pip install .[all]
     - name: Run tests
       run: |