Bump actions/checkout from 5 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 5 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v5...v6)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/actionlint.yml

@@ -6,7 +6,7 @@ jobs:
   actionlint:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           show-progress: false
       - uses: alphagov/govuk-infrastructure/.github/actions/actionlint@main

.github/workflows/copy-pr-template-to-dependabot-prs.yml

@@ -14,7 +14,7 @@ jobs:
     runs-on: ubuntu-latest
     if: github.actor == 'dependabot[bot]'
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: Post PR template as a comment
         uses: actions/github-script@v8

.github/workflows/rspec.yml

@@ -27,13 +27,13 @@ jobs:
         uses: alphagov/govuk-infrastructure/.github/actions/setup-redis@main
 
       - name: Checkout repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           repository: alphagov/short-url-manager
           ref: ${{ inputs.ref || github.ref }}
 
       - name: Checkout Publishing API (for Content Schemas)
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           repository: alphagov/publishing-api
           ref: ${{ inputs.publishingApiRef }}