Bump actions/checkout

Author: gliptak

.github/workflows/pypy.yml

@@ -16,7 +16,7 @@ jobs:
     name: ${{ matrix.python-version }}
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
 
       - name: Setup Python
         uses: actions/setup-python@v5