define python version for setup-python

v4 now requires a python version to be set

.github/workflows/docs.yml

@@ -49,6 +49,8 @@ jobs:
     # sphinx is a python package, so we need to setup python on this runner
     - name: Setup Python for Sphinx
       uses: actions/setup-python@v4
+      with:
+        python-version: 3.11
 
     # Runs sphinx-apidoc and sphinx-build in the docs/ directory
     #   sphinx-apidoc requires the python files to be packaged together