Update actions/checkout action to v6 (#263)

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

Author: renovate[bot]

.github/workflows/build.yml

@@ -16,7 +16,7 @@ jobs:
     runs-on: ubuntu-latest
     name: Flake Check
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
     - uses: DeterminateSystems/nix-installer-action@main
     - uses: cachix/cachix-action@v16
       with:
@@ -50,7 +50,7 @@ jobs:
         large-packages: true
         docker-images: true
         swap-storage: true
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
     - uses: DeterminateSystems/nix-installer-action@main
       with:
         extra-conf: |
@@ -93,7 +93,7 @@ jobs:
         large-packages: true
         docker-images: true
         swap-storage: true
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
     - uses: DeterminateSystems/nix-installer-action@main
       with:
         extra-conf: |

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

@@ -12,6 +12,6 @@ jobs:
         os: [ubuntu-latest]
         arch: [x86_64-linux]
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Check Nix flake inputs
         uses: DeterminateSystems/flake-checker-action@v12

.github/workflows/update-everything.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Install Determinate Nix
         uses: DeterminateSystems/determinate-nix-action@v3
       - name: Update flake.lock

.github/workflows/update-nixpkgs.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Install Determinate Nix
         uses: DeterminateSystems/determinate-nix-action@v3
       - name: Update flake.lock

.github/workflows/update-zed.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Install Determinate Nix
         uses: DeterminateSystems/determinate-nix-action@v3
       - name: Update flake.lock