ReactiveReceiverApplicationIntegrationTest is flaky

ReactiveReceiverApplicationIntegrationTest.testSample times out. See [job](https://github.com/GoogleCloudPlatform/spring-cloud-gcp/actions/runs/15212732242/job/42790649111)

Error: 9:784 [ERROR] Tests run: 1, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 8.361 s <<< FAILURE! -- in com.example.ReactiveReceiverApplicationIntegrationTest
Error: 9:784 [ERROR] com.example.ReactiveReceiverApplicationIntegrationTest.testSample -- Time elapsed: 6.026 s <<< ERROR!
java.lang.IllegalStateException: Timeout on blocking read for 5000000000 NANOSECONDS
at reactor.core.publisher.BlockingSingleSubscriber.blockingGet(BlockingSingleSubscriber.java:129)
at reactor.core.publisher.Mono.block(Mono.java:1807)
at org.springframework.test.web.reactive.server.DefaultWebTestClient$DefaultRequestBodyUriSpec.exchange(DefaultWebTestClient.java:369)
at com.example.ReactiveReceiverApplicationIntegrationTest.testSample(ReactiveReceiverApplicationIntegrationTest.java:72)
at java.base/java.lang.reflect.Method.invoke(Method.java:580)
at java.base/java.util.ArrayList.forEach(ArrayList.java:1597)
at java.base/java.util.ArrayList.forEach(ArrayList.java:1597)
Caused by: java.util.concurrent.TimeoutException: Timeout on blocking read for 5000000000 NANOSECONDS

Start with ReactiveReceiverApplicationIntegrationTest.testSample at line 72 and compare the failing CI job linked in the issue. Reproduce the timeout and trace the reactive request path; done means the integration test runs reliably without the blocking-read timeout.

Written by the indexing model from the issue text.