fix(notify-discord.yml): move DISCORD_WEBHOOK to env section for better clarity and maintainability

.github/workflows/notify-discord.yml

@@ -11,8 +11,9 @@ jobs:
     steps:
       - name: Send Discord message
         uses: Ilshidur/action-discord@master
+        env:
+          DISCORD_WEBHOOK: ${{ secrets.DISCORD_RELEASE_WEBHOOK }}
         with:
-          webhook: ${{ secrets.DISCORD_RELEASE_WEBHOOK }}
           message: |
             🚀 New release: **${{ github.event.release.name }}**
             ${{ github.event.release.html_url }}