Track merging PR #5336 into master branch

This issue is created to track the merging of [PR #5336](https://github.com/eggjs/egg/pull/5336) into the master branch. The PR fixes the xframe option type in `index.d.ts` as described in [issue #5306](https://github.com/eggjs/egg/issues/5306).

Please ensure that this PR is merged into the master branch after it has been merged into the 3.x branch.

PR details:
- **Title:** fix: xframe value type
- **User:** hongzzz
- **Number:** 5336
- **Description:** Fixes the xframe option type in `index.d.ts`.
- **Checklist:**
- [x] `npm test` passes
- [ ] Tests and/or benchmarks are included
- [ ] Documentation is changed or added
- [ ] Commit message follows commit guidelines

Linked issue: [#5306](https://github.com/eggjs/egg/issues/5306)