Bump actions/download-artifact from 5 to 6 in /.github/workflows

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

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

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/debug-artifacts-failure-safe.yml

@@ -79,7 +79,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Download all artifacts
-        uses: actions/download-artifact@v5
+        uses: actions/download-artifact@v6
       - name: Check expected artifacts exist
         run: |
           LANGUAGES="cpp csharp go java javascript python"

.github/workflows/debug-artifacts-safe.yml

@@ -73,7 +73,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Download all artifacts
-        uses: actions/download-artifact@v5
+        uses: actions/download-artifact@v6
       - name: Check expected artifacts exist
         run: |
           VERSIONS="stable-v2.20.3 default linked nightly-latest"