`invalid_payload` in `review-app-report`

See https://gitlab.com/gitlab-org/quality/toolbox/-/jobs/486857982:

124 $ bundle exec bin/failed_review_app_deploys_report --token=$GITLAB_BOT_ACCESS_TOKEN --hours=24 > review_apps_report.md
125 $ curl -X POST --data-urlencode 'payload={"channel": "#'"$SLACK_CHANNEL"'", "username": "Review App Reporter", "text": "'"$(cat review_apps_report.md)"'"' "$SLACK_WEBHOOK"
126   % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
127                                  Dload  Upload   Total   Spent    Left  Speed
128 100  4922    0    15  100  4907     64  21150 --:--:-- --:--:-- --:--:-- 21215
129 invalid_payload