Bump use of actions/checkout to avoid Node JS deprecations

.github/workflows/ci.yml

@@ -11,7 +11,7 @@ jobs:
         environment: ['3.8', '3.11', '3.10', '3.9', '3.7', '3.6', 'interpreter']
     steps:
       - name: Checkout code
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           submodules: recursive
 
@@ -36,7 +36,7 @@ jobs:
     runs-on: ubuntu-20.04
     steps:
       - name: Checkout code
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           submodules: recursive
 
@@ -53,7 +53,7 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           submodules: recursive