dependabot: bump actions/github-script from 6 to 8

Bumps [actions/github-script](https://github.com/actions/github-script) from 6 to 8.
- [Release notes](https://github.com/actions/github-script/releases)
- [Commits](actions/github-script@v6...v8)

---
updated-dependencies:
- dependency-name: actions/github-script
  dependency-version: '8'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/add-untriaged.yml

@@ -8,7 +8,7 @@ jobs:
   apply-label:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/github-script@v6
+      - uses: actions/github-script@v8
         with:
           script: |
             github.rest.issues.addLabels({

.github/workflows/delete_backport_branch.yml

@@ -12,7 +12,7 @@ jobs:
     if: startsWith(github.event.pull_request.head.ref,'backport/') || startsWith(github.event.pull_request.head.ref,'release-chores/')
     steps:
       - name: Delete merged branch
-        uses: actions/github-script@v7
+        uses: actions/github-script@v8
         with:
           script: |
             github.rest.git.deleteRef({