Fix GitHub dist workflow to not use new 3.10 version

Author: rlaphoenix

.github/workflows/dist.yml

@@ -17,7 +17,7 @@ jobs:
       - name: Set up Python
         uses: actions/setup-python@v2
         with:
-          python-version: '3.x'
+          python-version: '3.9.x'
       - name: Install Poetry
         uses: abatilo/actions-poetry@v2.1.0
         with: