ci: fix pydantic integration test to actually use local core (#1814)

Author: davidhewitt

.github/workflows/ci.yml

@@ -249,7 +249,7 @@ jobs:
 
       # Run pytest with lax xfail because we often add tests to pydantic
       # which xfail on a pending release of pydantic-core
-      - run: uv run pytest --override-ini=xfail_strict=False
+      - run: uv run --no-sync pytest --override-ini=xfail_strict=False
         working-directory: pydantic
         env:
           PYDANTIC_PRIVATE_ALLOW_UNHANDLED_SCHEMA_TYPES: 1