Bump actions/stale from 7 to 8 (open-telemetry#804)

Bumps [actions/stale](https://github.com/actions/stale) from 7 to 8.
- [Release notes](https://github.com/actions/stale/releases)
- [Changelog](https://github.com/actions/stale/blob/main/CHANGELOG.md)
- [Commits](actions/stale@v7...v8)

---
updated-dependencies:
- dependency-name: actions/stale
  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/stale.yml

@@ -10,7 +10,7 @@ jobs:
   stale:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/stale@v7
+      - uses: actions/stale@v8
         with:
           stale-pr-message: 'This PR was marked stale due to lack of activity. It will be closed in 7 days.'
           close-pr-message: 'Closed as inactive. Feel free to reopen if this PR is still being worked on.'