docs: Update stale documentation - .github/skills/experimental/mural/tests/corpus/README.md

## Stale Documentation Detected

**File:** `.github/skills/experimental/mural/tests/corpus/README.md`
**Current ms.date:** `2026-04-24`
**Age:** 115 days (threshold: 90 days)

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**Workflow Run:** https://github.com/microsoft/hve-core/actions/runs/32014593594
**Detection Date:** 2026-08-17

### Action Required
- [ ] Review and update this documentation file
- [ ] Update `ms.date` frontmatter to current date
- [ ] Verify technical accuracy of content
- [ ] Close this issue manually after fixes are merged

Open .github/skills/experimental/mural/tests/corpus/README.md and review its instructions for technical accuracy. Update the documentation where needed and set the ms.date frontmatter to the current date. Done means the file is accurate, dated, and the issue checklist can be completed after the changes are merged.

Written by the indexing model from the issue text.