Update actions/upload-artifact action to v6 (#35)

Co-authored-by: elastic-renovate-prod[bot] <174716857+elastic-renovate-prod[bot]@users.noreply.github.com>

Author: elastic-renovate-prod[bot]

.github/workflows/ci.yml

@@ -28,7 +28,7 @@ jobs:
         run: ./checks.sh
       - name: Store test results
         if: success() || failure()
-        uses: actions/upload-artifact@330a01c490aca151604b8cf639adc76d48f6c5d4 # v5
+        uses: actions/upload-artifact@b7c566a772e6b6bfb58ed0dc250532a479d7789f # v6
         with:
           name: test-results
           path: |