Docs build doesn't use tox, bump back to 3.8

.github/workflows/run_tests.yml

@@ -67,7 +67,7 @@ jobs:
       - uses: actions/checkout@v3
       - uses: conda-incubator/setup-miniconda@v2
         with:
-          python-version: 3.7
+          python-version: 3.8
       - name: Update pip and install dependencies
         shell: bash -l {0}
         run: |