Eligibility
This is a straightforward accessibility fix (replacing incorrect aria-selected with correct aria-expanded on a toggle button) with no runtime behavior impact. However, the file is owned by @elastic/search-kibana and the author is not a designated code owner, so the designated team should review.

Notes:
@seialkali isn't a code owner for 1 file:

• x-pack/platform/packages/shared/kbn-search-index-documents/components/result/result.tsx (owned by @elastic/search-kibana)