ci: bump actions/checkout to v4

Author: checkout‑bot

.github/workflows/tests.yaml

@@ -13,7 +13,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Set up Docker
         uses: docker/setup-buildx-action@v2

.github/workflows/update.yaml

@@ -17,7 +17,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
 
       - name: Get version
         id: versions_step