dependabot: bump actions/github-script from 5 to 7 (#695)

Bumps [actions/github-script](https://github.com/actions/github-script) from 5 to 7.
- [Release notes](https://github.com/actions/github-script/releases)
- [Commits](actions/github-script@v5...v7)

---
updated-dependencies:
- dependency-name: actions/github-script
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/delete_backport_branch.yml

@@ -12,7 +12,7 @@ jobs:
     if: github.repository == 'opensearch-project/job-scheduler' && startsWith(github.event.pull_request.head.ref,'backport/')
     steps:
       - name: Delete branch
-        uses: actions/github-script@v5
+        uses: actions/github-script@v7
         with:
           script: |
             github.rest.git.deleteRef({