chore: bump Python version in publish workflow (#233)

Author: bfabio

.github/workflows/publish.yml

@@ -13,7 +13,7 @@ jobs:
       - uses: actions/checkout@v2
       - uses: actions/setup-python@v2
         with:
-          python-version: '3.8'
+          python-version: '3.9'
 
       - run: pip install -r requirements.txt
       - run: sphinx-build docs/standard build -c .