Bump actions/checkout from 4 to 5 in /reuse

Bumps [actions/checkout](https://github.com/actions/checkout) from 4 to 5.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v4...v5)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '5'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

reuse/action.yml

@@ -27,7 +27,7 @@ runs:
   using: composite
   steps:
   - name: Checkout
-    uses: actions/checkout@v4
+    uses: actions/checkout@v5
     with:
       path: reuse-tool
       repository: UoMResearchIT/reuse-tool