⬆️ Bump actions/checkout from 3 to 4 (#98)

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/tests.yml

@@ -17,7 +17,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Set up Python 3.8
       uses: actions/setup-python@v4
       with:
@@ -33,7 +33,7 @@ jobs:
         python-version: ['pypy-3.8', '3.8', '3.9', '3.10', '3.11']
 
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Set up Python ${{ matrix.python-version }}
       uses: actions/setup-python@v4
       with:
@@ -69,7 +69,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - name: Checkout source
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
     - name: Set up Python
       uses: actions/setup-python@v4
       with: