ci: upgrade Redis action and specify Redis version

Author: dbohdan

.github/workflows/tox.yml

@@ -29,7 +29,9 @@ jobs:
         with:
           python-version: ${{ matrix.python }}
       - name: Start Redis
-        uses: supercharge/[email protected]
+        uses: supercharge/[email protected]
+        with:
+          redis-version: 6
       - name: Install Tox and any other packages
         run: pip install tox
       - name: Run Tox