chore(deps): bump actions/download-artifact in the gha-updates group (Lightning-AI#741)

Bumps the gha-updates group with 1 update: [actions/download-artifact](https://github.com/actions/download-artifact).


Updates `actions/download-artifact` from 5 to 6
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v5...v6)

---
updated-dependencies:
- dependency-name: actions/download-artifact
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: gha-updates
...

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Author: dependabot[bot]

.github/workflows/docs-build.yml

@@ -20,7 +20,7 @@ jobs:
     steps:
       - uses: actions/checkout@v5 # deploy needs git credentials
       - name: Download prepared docs
-        uses: actions/download-artifact@v5
+        uses: actions/download-artifact@v6
         with:
           name: docs-html-${{ github.sha }}
           path: docs/build/html