Update actions/checkout action to v5

Author: renovate[bot]

.github/workflows/ci.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - name: Checkout repository
-      uses: actions/checkout@v4
+      uses: actions/checkout@v5
     - name: Install Nix
       uses: DeterminateSystems/nix-installer-action@main
    #  - uses: cachix/cachix-action@v12

.github/workflows/update-flake-lock.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v5
       - name: Install Nix
         uses: DeterminateSystems/nix-installer-action@main
       - name: Update flake.lock