Bump guardian/actions-riff-raff from 2 to 4

Bumps [guardian/actions-riff-raff](https://github.com/guardian/actions-riff-raff) from 2 to 4.
- [Release notes](https://github.com/guardian/actions-riff-raff/releases)
- [Commits](guardian/actions-riff-raff@v2...v4)

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

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

.github/workflows/ci.yml

@@ -85,7 +85,7 @@ jobs:
           role-to-assume: ${{ secrets.GU_RIFF_RAFF_ROLE_ARN }}
 
       - name: Upload to Riff-Raff
-        uses: guardian/actions-riff-raff@v2
+        uses: guardian/actions-riff-raff@v4
         with:
           app: support-reminders
           configPath: ./riff-raff.yaml