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](actions/checkout@v3...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/documentation.yml

@@ -6,7 +6,7 @@ jobs:
   docs:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
       with:
         ref: ${{ github.event.pull_request.head.ref }}
     - uses: terraform-docs/[email protected]

.github/workflows/push-terraform-module-version.yml

@@ -7,7 +7,7 @@ jobs:
   push-terraform-module-version:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: ministryofjustice/cloud-platform-environments/cmd/push-terraform-module-version@main
         env:
           # see https://github.com/ministryofjustice/cloud-platform-go-get-module/

.github/workflows/unit.yml

@@ -7,7 +7,7 @@ jobs:
     name: Run Terratest Unit Tests
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: hashicorp/setup-terraform@v2
         with:
           terraform_version: 1.2.5