build: fix cache key in trivydb creation workflow

Match the one used on cache restore.

.github/workflows/trivydb-cache.yaml

@@ -36,4 +36,4 @@ jobs:
         uses: actions/cache/save@1bd1e32a3bdc45362d1e726936510720a7c30a57 # v4.2.0
         with:
           path: ${{ github.workspace }}/.cache/trivy
-          key: cache-trivy-${{ steps.date.outputs.date }}
+          key: trivy-cache-${{ steps.date.outputs.date }}