fix: set mattermost payload

.github/workflows/stress.yml

@@ -49,10 +49,11 @@ jobs:
         | Entries: 1M - Workers: 50 - Batch: 1k - Batches: 20 | ${{ steps.e_1m_w_50_b_1k_bs_20.outcome }} | ${{ env.duration_2 }}s |\n
         | Entries: 1M - Workers: 100 - Batch: 1k - Batches: 10 | ${{ steps.e_1m_w_100_b_1k_bs_10.outcome }} | ${{ env.duration_3 }}s |\n
         **Check details [here](${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }})**
-        \"}" > mattermost.json
+        \"}" > mattermost.json && echo MM_PAYLOAD=$(cat mattermost.json) >> $GITHUB_ENV
     - name: Notify on immudb channel on Mattermost
       if: github.event.schedule == '0 0 * * *'
       uses: mattermost/action-mattermost-notify@master
       with:
         MATTERMOST_WEBHOOK_URL: ${{ secrets.MATTERMOST_WEBHOOK_URL }}
         MATTERMOST_CHANNEL: 'immudb-tests'
+        PAYLOAD: ${{ env.MM_PAYLOAD }}