test: JSON payload + literal-newline message

Author: carole-lavillonniere

.github/workflows/weekly-release.yml

@@ -99,7 +99,7 @@ jobs:
       - name: "Send Message"
         uses: slackapi/slack-github-action@dcb1066f776dd043e64d0e8ba94ca15cc7e1875d # v4.0.0
         env:
-          MESSAGE: ":test_tube: *TEST -- please ignore* :test_tube:\n\nVerifying that COSY_WEBHOOK_URL is configured for `lambda-runtime-init` after it was found empty. No release was affected. <${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}|Run>"
+          MESSAGE: ':test_tube: *TEST -- please ignore* :test_tube:\n\nVerifying that COSY_WEBHOOK_URL is configured for `lambda-runtime-init` after it was found empty. No release was affected. <${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}|Run>'
         with:
           webhook: ${{ secrets.COSY_WEBHOOK_URL }}
           webhook-type: incoming-webhook
@@ -108,8 +108,11 @@ jobs:
           # outcome we cannot afford.
           errors: true
           payload: |
-            blocks:
-              - type: "section"
-                text:
-                  type: "mrkdwn"
-                  text: "${{ env.MESSAGE }}"
+            {
+              "blocks": [
+                {
+                  "type": "section",
+                  "text": { "type": "mrkdwn", "text": "${{ env.MESSAGE }}" }
+                }
+              ]
+            }