Update actions/checkout action to v4 (#34)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

.github/workflows/codeql-analysis.yml

@@ -38,7 +38,7 @@ jobs:
 
     steps:
     - name: Checkout repository
-      uses: actions/checkout@v3
+      uses: actions/checkout@3df4ab11eba7bda6032a0b82a6bb43b11571feac # v4
 
     # Initializes the CodeQL tools for scanning.
     - name: Initialize CodeQL

.github/workflows/main.yml

@@ -8,7 +8,7 @@ jobs:
     name: Lint report
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@3df4ab11eba7bda6032a0b82a6bb43b11571feac # v4
       - name: Install tox
         run: pip install tox
       - name: Run tests using tox
@@ -18,7 +18,7 @@ jobs:
     name: Static analysis
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@3df4ab11eba7bda6032a0b82a6bb43b11571feac # v4
       - name: Install tox
         run: pip install tox
       - name: Run tests using tox
@@ -28,7 +28,7 @@ jobs:
     name: Unit tests
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@3df4ab11eba7bda6032a0b82a6bb43b11571feac # v4
       - name: Install tox
         run: pip install tox
       - name: Run tests using tox
@@ -39,7 +39,7 @@ jobs:
     runs-on: ubuntu-22.04
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@3df4ab11eba7bda6032a0b82a6bb43b11571feac # v4
       - name: Setup operator environment
         uses: charmed-kubernetes/actions-operator@main
         with:

.github/workflows/publish.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@3df4ab11eba7bda6032a0b82a6bb43b11571feac # v4
         with:
           fetch-depth: 0