CI: bump actions/checkout to v4

Author: kbdharun

.github/workflows/publish.yml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-20.04
 
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
 
     - name: Set up Python
       uses: actions/setup-python@v4

.github/workflows/test.yml

@@ -11,7 +11,7 @@ jobs:
         python-version: ['3.8', '3.9', '3.10', '3.11', 'pypy3.9', 'pypy3.10']
 
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
 
     - name: Set up Python ${{ matrix.python-version }}
       uses: actions/setup-python@v4