ci: bump actions/upload-artifact from 4 to 6

Bumps [actions/upload-artifact](https://github.com/actions/upload-artifact) from 4 to 6.
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](actions/upload-artifact@v4...v6)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/terminal-bench.yaml

@@ -78,7 +78,7 @@ jobs:
     # uploads results if run fails as well to allow for easy log inspection
     - name: Upload results
       if: always()
-      uses: actions/upload-artifact@v4
+      uses: actions/upload-artifact@v6
       with:
         name: benchmark-results
         path: terminal-bench-test/runs/