Use Dendrite flow to trigger Docker flow for :main

.github/workflows/docker.yml

@@ -3,11 +3,12 @@
 name: "Docker Hub"
 
 on:
-  release:
+  release: # A GitHub release was published
     types: [published]
-  push:
-    branches:
-      - main
+  workflow_run: # The Dendrite pipeline completed successfully on main
+    workflows: [Dendrite]
+    types: [completed]
+    branches: [main]
 
 env:
   DOCKER_NAMESPACE: matrixdotorg
@@ -41,7 +42,9 @@ jobs:
           password: ${{ secrets.GITHUB_TOKEN }}
 
       - name: Build monolith image
-        if: ${{ github.event_name == 'push' }}
+        if: >-
+          github.event_name == 'workflow_run' &&
+          github.event.workflow_run.conclusion == 'success'
         id: docker_build_monolith
         uses: docker/build-push-action@v2
         with:
@@ -56,7 +59,7 @@ jobs:
             ghcr.io/${{ GHCR_NAMESPACE }}/dendrite-monolith:main
 
       - name: Build release monolith image
-        if: ${{ github.event_name == 'release' }}
+        if: github.event_name == 'release'
         id: docker_build_monolith
         uses: docker/build-push-action@v2
         with:
@@ -97,7 +100,9 @@ jobs:
           password: ${{ secrets.GITHUB_TOKEN }}
 
       - name: Build polylith image
-        if: ${{ github.event_name == 'push' }}
+        if: >-
+          github.event_name == 'workflow_run' &&
+          github.event.workflow_run.conclusion == 'success'
         id: docker_build_polylith
         uses: docker/build-push-action@v2
         with: