Polish usage of spring-boot-testcontainers

[quaff]

No description provided.

[rwinch]

Thanks for the pull request @quaff! Could you please fix the build failure?

Caused by: org.gradle.api.internal.tasks.compile.CompilationFailedException: Compilation failed; see the compiler output below.
/home/runner/work/spring-session/spring-session/spring-session-samples/spring-session-sample-boot-reactive-redis-indexed/src/test/java/com/example/TestcontainersConfig.java:30: error: cannot find symbol
	RedisContainer redisContainer() {
	^
  symbol:   class RedisContainer
  location: class TestcontainersConfig
/home/runner/work/spring-session/spring-session/spring-session-samples/spring-session-sample-boot-reactive-redis-indexed/src/test/java/com/example/TestcontainersConfig.java:31: error: cannot find symbol
		return new RedisContainer(DockerImageName.parse("redis:6.2.6"));
		           ^
  symbol:   class RedisContainer
  location: class TestcontainersConfig
2 errors
	at org.gradle.api.internal.tasks.compile.JdkJavaCompiler.execute(JdkJavaCompiler.java:84)
	at org.gradle.api.internal.tasks.compile.JdkJavaCompiler.execute(JdkJavaCompiler.java:46)
	at org.gradle.api.internal.tasks.compile.NormalizingJavaCompiler.delegateAndHandleErrors(NormalizingJavaCompiler.java:98)

[quaff]

@rwinch Fixed now.

The failed test passes on my machine.

> Task :spring-session-data-redis:integrationTest

ReactiveRedisIndexedSessionRepositoryITests > findByPrincipalNameWhenExpireKeyEventThenRemovesIndexAndSessionExpiredEvent() FAILED
    java.lang.ClassCastException at ReactiveRedisIndexedSessionRepositoryITests.java:171