DEV: Have workflow only run if it finds changes (#159)

We want to make sure the validate_pr workflow runs only if the
update_docs workflow made a PR.

Author: blake-discourse

.github/workflows/update_docs.yml

@@ -87,6 +87,7 @@ jobs:
           fi
 
       - name: Create PR
+        id: create-pr
         uses: peter-evans/create-pull-request@v5
         with:
           path: discourse_api_docs
@@ -97,3 +98,12 @@ jobs:
           author: discoursebuild <build@discourse.org>
           body: |
             Updates Documentation with changes from Discourse core
+
+      - name: Trigger validation
+        if: steps.create-pr.outputs.pull-request-number
+        run: |
+          curl -X POST \
+            -H "Accept: application/vnd.github.v3+json" \
+            -H "Authorization: token ${{ secrets.GITHUB_TOKEN }}" \
+            https://api.github.com/repos/${{ github.repository }}/dispatches \
+            -d '{"event_type":"docs-updated","client_payload":{"branch":"update-documentation"}}'

.github/workflows/validate_pr.yml

@@ -5,10 +5,8 @@ on:
     types: [opened, synchronize, reopened]
     paths:
       - 'openapi.json'
-  workflow_run:
-    workflows: ["Update Docs"]
-    types: [completed]
-    branches: [main]
+  repository_dispatch:
+    types: [docs-updated]
 
 jobs:
   validate-openapi:
@@ -22,11 +20,11 @@ jobs:
         with:
           fetch-depth: 0
 
-      - name: Checkout workflow run
-        if: github.event_name == 'workflow_run'
+      - name: Checkout docs-updated branch
+        if: github.event_name == 'repository_dispatch'
         uses: actions/checkout@v4
         with:
-          ref: ${{ github.event.workflow_run.head_branch }}
+          ref: ${{ github.event.client_payload.branch }}
           fetch-depth: 0
 
       - name: Start Swagger Validator