build(deps): bump actions/download-artifact from 4 to 8

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 4 to 8.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](https://github.com/actions/download-artifact/compare/v4...v8)

---
updated-dependencies:
- dependency-name: actions/download-artifact
  dependency-version: '8'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

.github/workflows/benchstat.yml

@@ -69,11 +69,11 @@ jobs:
       - name: Install benchstat
         run: go get -u golang.org/x/perf/cmd/benchstat
       - name: Download Incoming
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v8
         with:
           name: bench-incoming
       - name: Download Current
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v8
         with:
           name: bench-current
       - name: Benchstat Results