Updates release workflow to use correct tag for release artefacts. (#1033)

## PR Type
- [x] Feature
- [ ] Hotfix
- [ ] Release
- [ ] Documentation

---

## Checklist
- [x] Code builds locally
- [ ] Tests added or updated
- [x] CI is green
- [ ] Peer review completed

---

### UAT
- [ ] Required → completed
- [x] Not required (explain below)


This is a change to the Pipeline and doesn't require UAT

Author: carlsixsmith-moj

.github/workflows/create-release.yml

@@ -52,6 +52,7 @@ jobs:
         with:
           tag_name: ${{ steps.version.outputs.tag }}
           name: Release ${{ steps.version.outputs.tag }}
+          target_commitish: ${{ github.event.pull_request.merge_commit_sha }}
           files: "${{ steps.version.outputs.tag }}.zip"
           draft: false
           prerelease: false