Try square braces.

Author: desrosj

.github/workflows/slack-notifications.yml

@@ -155,10 +155,11 @@ jobs:
         run: |
           PAYLOAD="$( jq \
             -n \
+            --arg workflow_name "${GITHUB_WORKFLOW}" \
             --arg ref_name "${CURRENT_BRANCH}" \
             --arg run_url "https://github.com/WordPress/wordpress-develop/actions/runs/${GITHUB_RUN_ID}/attempts/${GITHUB_RUN_ATTEMPT}" \
             --arg commit_message "${COMMIT_MSG}" \
-            '{ref_name: $ref_name, run_url: $run_url, commit_message: $commit_message}'
+            '[{workflow_name: $workflow_name, ref_name: $ref_name, run_url: $run_url, commit_message: $commit_message}]'
           )"
           echo "payload=$PAYLOAD" >> "$GITHUB_OUTPUT"
         env: