CI: generate openapi contract before asking for contract diff

.github/workflows/bump.yml

@@ -31,7 +31,26 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
+      - name: Set up docker Buildx
+        uses: docker/setup-buildx-action@v3
+      - name: Build docker image
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          file: ./api/Dockerfile
+          tags: local:latest
+          load: true
+          cache-from: type=gha
+          cache-to: type=gha,mode=max
+          push: false
+      - name: Generate OpenAPI contract
+        uses: addnab/docker-run-action@v3
+        with:
+          image: local:latest
+          options: -v ${{ github.workspace }}:/work
+          run: |
+            php bin/console api:openapi:export > /work/docs/openapi.json
       - name: Comment pull request with API diff
         uses: bump-sh/github-action@v1
         with: