Update actions/checkout action to v4

.github/workflows/agent-tox.yml

@@ -20,7 +20,7 @@ jobs:
       matrix:
         python: ["3.8", "3.10"]
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Set up Python
       uses: actions/setup-python@v5
       with:

.github/workflows/server-charm-check-libs.yml

@@ -14,7 +14,7 @@ jobs:
     runs-on: [self-hosted, linux, X64]
     steps:
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
         with:
           fetch-depth: 0  
       - name: Check libraries

.github/workflows/server-charm-release-edge.yml

@@ -30,7 +30,7 @@ jobs:
               mirrors = ["https://github-runner-dockerhub-cache.canonical.com:5000"]
 
       - name: Checkout repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Log in to the Container registry
         uses: docker/login-action@65b78e6e13532edd9afa3aa52ac7964289d1a9c1

.github/workflows/server-tox.yml

@@ -20,7 +20,7 @@ jobs:
       matrix:
         python: ["3.8", "3.10"]
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Set up Python
       uses: actions/setup-python@v5
       with: