DEV: Attempt to get workflow to trigger on PR (#161)

Since we changed the validation workflow to trigger on
pull_request_target, it will now be triggered automatically by the
GitHub event that is fired when the create-pull-request action
successfully opens a pull request. The manual repository_dispatch is no
longer needed.

Hopefully this works!

Author: blake-discourse

.github/workflows/update_docs.yml

@@ -99,11 +99,3 @@ jobs:
           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

@@ -1,30 +1,25 @@
 name: Validate PR Documentation
 
 on:
-  pull_request:
+  pull_request_target:
     types: [opened, synchronize, reopened]
     paths:
       - 'openapi.json'
-  repository_dispatch:
-    types: [docs-updated]
 
 jobs:
   validate-openapi:
     runs-on: ubuntu-latest
     timeout-minutes: 10
 
     steps:
-      - name: Checkout PR
-        if: github.event_name == 'pull_request'
+      - name: Checkout PR Code
         uses: actions/checkout@v4
         with:
-          fetch-depth: 0
-
-      - name: Checkout docs-updated branch
-        if: github.event_name == 'repository_dispatch'
-        uses: actions/checkout@v4
-        with:
-          ref: ${{ github.event.client_payload.branch }}
+          # This is critical for pull_request_target. It ensures we checkout
+          # the code from the PR, not the base branch.
+          ref: ${{ github.event.pull_request.head.sha }}
+          # fetch-depth: 0 is not strictly needed for validation, but kept it
+          # in case your validation scripts need the full git history.
           fetch-depth: 0
 
       - name: Start Swagger Validator