actions: fix quoting on the 5th try

.github/workflows/rust.yml

@@ -54,7 +54,7 @@ jobs:
           CHANNEL_ID: ${{ secrets.ANNOUNCEMENT_CHANNEL_ID }}
           OLD_COMMIT_SHA: ${{ github.event.before }}
         run: |
-          msg=$(git log --no-decorate ${OLD_COMMIT_SHA}..)
+          msg=$(git log --no-decorate ${OLD_COMMIT_SHA}.. | sed -z 's/\n/\\n/g')
           curl https://discord.com/api/channels/${CHANNEL_ID}/messages -H "Authorization: Bot ${DISCORD_TOKEN}" -X POST -H "Content-Type: application/json" -d '{"content": "Deploying new version of the bot...\nNew changes:\n\n' "$msg" '"}'
 
       - name: Fetch the binary