Bump actions/checkout from 4.1.7 to 4.2.1

Bumps [actions/checkout](https://github.com/actions/checkout) from 4.1.7 to 4.2.1.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v4.1.7...v4.2.1)

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

Signed-off-by: dependabot[bot] <[email protected]>

.github/workflows/build.yml

@@ -11,7 +11,7 @@ jobs:
     name: nix (${{ matrix.os }})
     runs-on: ${{ matrix.os }}
     steps:
-      - uses: actions/checkout@v4.1.7
+      - uses: actions/checkout@v4.2.1
       - uses: DeterminateSystems/nix-installer-action@main
       - uses: DeterminateSystems/magic-nix-cache-action@main
       - run: nix --show-trace build -f . custom jacobi_tools

.github/workflows/formatting.yml

@@ -4,7 +4,7 @@ jobs:
   prettier:
     runs-on: ubuntu-24.04
     steps:
-      - uses: actions/checkout@v4.1.7
+      - uses: actions/checkout@v4.2.1
       - uses: cachix/install-nix-action@V27
         with:
           extra_nix_config: |
@@ -14,7 +14,7 @@ jobs:
   nixpkgs-fmt:
     runs-on: ubuntu-24.04
     steps:
-      - uses: actions/checkout@v4.1.7
+      - uses: actions/checkout@v4.2.1
       - uses: cachix/install-nix-action@V27
         with:
           extra_nix_config: |

.github/workflows/statix.yml

@@ -4,7 +4,7 @@ jobs:
   statix:
     runs-on: ubuntu-24.04
     steps:
-      - uses: actions/checkout@v4.1.7
+      - uses: actions/checkout@v4.2.1
       - uses: cachix/install-nix-action@V27
         with:
           extra_nix_config: |