actions: confirm swagger.json is updated

.github/workflows/swagger.yml

@@ -0,0 +1,18 @@
+name: Swagger
+on: [push, pull_request]
+jobs:
+  swagger:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.11.x'
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install .
+      - name: Validate swagger.json
+        run: |
+          diff -u swagger.json <(swagger)