flaky test(datastore-basic-sample): DatastoreBookshelfExampleIntegrationTests

Test failed with assertion error:

```
Error: 8:907 [ERROR] Errors:
Error: 8:908 [ERROR] DatastoreBookshelfExampleIntegrationTests.findAllBooksTest:87 » ConditionTimeout Assertion condition defined as a Lambda expression in com.example.DatastoreBookshelfExampleIntegrationTests
Expecting actual:
"[Book***id=5786403086532608, title='Ubik', author='Philip K. Dick', year=1969***, Book***id=6555614549377024, title='The Crack in Space', author='Philip K. Dick', year=1966***]"
to contain:
"title='The Moon Is a Harsh Mistress', author='Robert A. Heinlein', year=1966" within 15 seconds.
20:33:58:908 [INFO]
Error: 8:908 [ERROR] Tests run: 7, Failures: 0, Errors: 1, Skipped: 0
```

Full log [here](https://github.com/GoogleCloudPlatform/spring-cloud-gcp/actions/runs/15935307683/job/44953697344?pr=3902)