ci: add flag to integration tests to mitigate schema changes (#1480)

Author: davidhewitt

.github/workflows/ci.yml

@@ -245,6 +245,8 @@ jobs:
         # which xfail on a pending release of pydantic-core
       - run: pdm run pytest --override-ini=xfail_strict=False
         working-directory: pydantic
+        env:
+          PYDANTIC_PRIVATE_ALLOW_UNHANDLED_SCHEMA_TYPES: 1
 
   lint:
     runs-on: ubuntu-latest