Update to setup-python v4. Fixes jaraco/skeleton#65.

Author: jaraco

.github/workflows/main.yml

@@ -18,7 +18,7 @@ jobs:
     steps:
       - uses: actions/checkout@v3
       - name: Setup Python
-        uses: actions/setup-python@v3
+        uses: actions/setup-python@v4
         with:
           python-version: ${{ matrix.python }}-dev
       - name: Install tox