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/flake.yml

@@ -8,7 +8,7 @@ jobs:
     name: Build Nix targets
     runs-on: ubuntu-22.04
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Check Nix flake inputs
         uses: DeterminateSystems/flake-checker-action@v5 # This action
       - name: Install Nix

.github/workflows/flakehub-backfill.yaml

@@ -15,7 +15,7 @@ jobs:
       id-token: "write"
       contents: "read"
     steps:
-      - uses: "actions/checkout@v3"
+      - uses: "actions/checkout@v4"
         with:
           ref: "refs/tags/${{ inputs.tag }}"
       - uses: "DeterminateSystems/nix-installer-action@main"

.github/workflows/flakehub-publish-tagged.yml

@@ -10,7 +10,7 @@ jobs:
       id-token: "write"
       contents: "read"
     steps:
-      - uses: "actions/checkout@v3"
+      - uses: "actions/checkout@v4"
       - uses: "DeterminateSystems/nix-installer-action@main"
       - uses: "DeterminateSystems/flakehub-push@main"
         with:

.github/workflows/unit-tests.yml

@@ -32,7 +32,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@v1