Merge pull request matplotlib#23071 from QuLogic/fix-contourpy-test

Fix installing contourpy on CI

Author: oscargus

.github/workflows/tests.yml

@@ -161,8 +161,8 @@ jobs:
 
           # Install dependencies from PyPI.
           python -m pip install --upgrade $PRE \
-            contourpy>=1.0.1 cycler fonttools kiwisolver numpy packaging pillow pyparsing \
-            python-dateutil setuptools-scm \
+            'contourpy>=1.0.1' cycler fonttools kiwisolver numpy packaging \
+            pillow pyparsing python-dateutil setuptools-scm \
             -r requirements/testing/all.txt \
             ${{ matrix.extra-requirements }}