split openapi workflows between pull request and merge

.github/workflows/openapi/pull-request.yml

@@ -0,0 +1,72 @@
+name: OpenAPI Check
+on:
+  pull_request:
+
+jobs:
+  ancestor:
+    name: Common Ancestor
+    runs-on: ubuntu-latest
+    outputs:
+      base_ref: ${{ steps.ancestor.outputs.base_ref }}
+    steps:
+    - name: Checkout Repository
+      uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+      with:
+        ref: ${{ github.event.pull_request.head.sha }}
+        repository: ${{ github.event.pull_request.head.repo.full_name }}
+        fetch-depth: 0
+    - name: Search History
+      id: ancestor
+      run: |
+        git remote add upstream https://github.com/${{ github.event.pull_request.base.repo.full_name }}
+        git fetch --prune --progress --no-recurse-submodules upstream +refs/heads/*:refs/remotes/upstream/* +refs/tags/*:refs/tags/*
+
+        ANCESTOR_REF=$(git merge-base upstream/${{ github.base_ref }} HEAD)
+
+        echo "ref: ${ANCESTOR_REF}"
+
+        echo "base_ref=${ANCESTOR_REF}" >> "$GITHUB_OUTPUT"
+
+  head:
+    name: Head Artifact
+    uses: ./.github/workflows/openapi/__generate.yml
+    with:
+      ref: ${{ github.event.pull_request.head.sha }}
+      repository: ${{ github.event.pull_request.head.repo.full_name }}
+      artifact: openapi-head
+
+  base:
+    name: Base Artifact
+    uses: ./.github/workflows/openapi/__generate.yml
+    needs:
+    - ancestor
+    with:
+      ref: ${{ needs.ancestor.outputs.base_ref }}
+      repository: ${{ github.event.pull_request.base.repo.full_name }}
+      artifact: openapi-base
+
+  diff:
+    name: Generate Report
+    runs-on: ubuntu-latest
+    needs:
+    - head
+    - base
+    steps:
+    - name: Download Head
+      uses: actions/download-artifact@3e5f45b2cfb9172054b4087a40e8e0b5a5461e7c # v8.0.1
+      with:
+        name: openapi-head
+        path: openapi-head
+    - name: Download Base
+      uses: actions/download-artifact@3e5f45b2cfb9172054b4087a40e8e0b5a5461e7c # v8.0.1
+      with:
+        name: openapi-base
+        path: openapi-base
+    - name: Detect Changes
+      uses: jellyfin/openapi-diff-action@9274f6bda9d01ab091942a4a8334baa53692e8a4 # v1.0.0
+      id: openapi-diff
+      with:
+        old-spec: openapi-base/openapi.json
+        new-spec: openapi-head/openapi.json
+        markdown: openapi-changelog.md
+        github-token: ${{ secrets.GITHUB_TOKEN }}