Update README.md to fix setup-python version in example (actions#368)

Author: tiwarishub

README.md

@@ -249,10 +249,10 @@ steps:
 **Caching poetry dependencies:**
 ```yaml
 steps:
-- uses: actions/checkout@v2
+- uses: actions/checkout@v3
 - name: Install poetry
   run: pipx install poetry
-- uses: actions/setup-python@v2
+- uses: actions/setup-python@v3
   with:
     python-version: '3.9'
     cache: 'poetry'