chore(deps): bump actions/checkout from 3 to 4

Bumps [actions/checkout](https://github.com/actions/checkout) from 3 to 4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](https://github.com/actions/checkout/compare/v3...v4)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/cachix.yml

@@ -31,7 +31,7 @@ jobs:
           remove-haskell: true
           remove-codeql: true
 
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         name: Checkout
 
       - uses: cachix/install-nix-action@v20

.github/workflows/check-docs.yml

@@ -34,7 +34,7 @@ jobs:
             experimental-features = nix-command flakes
           nix_path: nixpkgs=channel:nixos-unstable
 
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         name: Checkout
 
       - name: Set default git branch (to reduce log spam)

.github/workflows/check.yml

@@ -14,7 +14,7 @@ jobs:
     name: Validate Flake
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: cachix/install-nix-action@v20
         with:
           extra_nix_config: |
@@ -25,7 +25,7 @@ jobs:
     name: Formatting via Alejandra
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: cachix/install-nix-action@v20
         with:
           install_url: https://nixos.org/nix/install

.github/workflows/manual.yml

@@ -24,7 +24,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Install Nix
         uses: cachix/install-nix-action@v18