Bump actions/checkout from 2 to 4

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 to 4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v2...v4)

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

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

.github/workflows/check.yml

@@ -6,7 +6,7 @@ jobs:
   tests:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
       with:
           fetch-depth: 0
     - uses: cachix/install-nix-action@v17

.github/workflows/format.yml

@@ -6,7 +6,7 @@ jobs:
   tests:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
       with:
           fetch-depth: 0
     - uses: cachix/install-nix-action@v17

.github/workflows/statix.yml

@@ -6,7 +6,7 @@ jobs:
   tests:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
       with:
           fetch-depth: 0
     - uses: cachix/install-nix-action@v17

.github/workflows/update.yml

@@ -15,7 +15,7 @@ jobs:
       # - uses: styfle/[email protected]
       #   with:
       #     access_token: ${{ github.token }}
-      - uses: actions/checkout@v2.4.0
+      - uses: actions/checkout@v4
         with:
           persist-credentials: false # otherwise, the token used is the GITHUB_TOKEN, instead of your personal token
           fetch-depth: 0 # otherwise, you will failed to push refs to dest repo