Add or update websockets integration test

[bclozel]

A failure has been reported on Spring Boot 3.2 AOT smoke tests. We should update our integration tests on the 1.2.x branch to test for that case.

See https://ci.spring.io/teams/spring-aot-smoke-tests/pipelines/spring-aot-smoke-tests-3.2.x/jobs/graphql-webmvc-app-test/builds/1

[bclozel]

Superseded by spring-projects/spring-boot#37892