Update actions/checkout action to v4 (#5409)

Signed-off-by: milkmaker <milkmaker@mailcow.de>
Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

.github/workflows/image_builds.yml

@@ -28,7 +28,7 @@ jobs:
           - "watchdog-mailcow"
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Setup Docker
         run: |
           curl -sSL https://get.docker.com/ | CHANNEL=stable sudo sh

.github/workflows/pr_to_nightly.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           fetch-depth: 0
       - name: Run the Action

.github/workflows/rebuild_backup_image.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Set up QEMU
         uses: docker/setup-qemu-action@v2

.github/workflows/update_postscreen_access_list.yml

@@ -15,7 +15,7 @@ jobs:
    runs-on: ubuntu-latest
    steps:
     - name: Checkout
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
 
     - name: Generate postscreen_access.cidr
       run: |