report master/release-* failures (mattermost#25197)

.github/workflows/workflow-failure-check.yml

@@ -0,0 +1,19 @@
+name: Report on master workflow failure
+on:
+  workflow_run:
+    workflows: [Server CI Master, Web App CI Master]
+    types: [completed]
+
+jobs:
+  on-failure:
+    runs-on: ubuntu-latest
+    if: github.event.workflow_run.conclusion == 'failure'
+    steps:
+      name: Report failure
+        run: |
+          curl \
+            --fail \
+            -X POST \
+            -H "Content-Type: application/json" \
+            -d "{\"text\":\"#### ⚠️  ${{github.repository}}/${{ github.event.workflow_run.head_branch }} - ${{github.event.workflow_run.name}} build failure ⚠️\\nThe build is failing: [view failure](${{github.server_url}}/${{github.repository}}/actions/runs/${{github.event.workflow_run.id}}).\\n\"}" \
+            ${{ secrets.MM_COMMUNITY_DEVELOPERS_INCOMING_WEBHOOK_FROM_GH_ACTIONS }}