Fix Spring Data Cassandra auto-configure condition

Update `CassandraDataAutoConfiguration` do that it's only applied when
a `Cluster` bean is found.

Fixes gh-16971

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/data/cassandra/CassandraDataAutoConfiguration.java

@@ -28,6 +28,7 @@ import org.springframework.boot.autoconfigure.AutoConfigureAfter;
 import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
 import org.springframework.boot.autoconfigure.cassandra.CassandraAutoConfiguration;
 import org.springframework.boot.autoconfigure.cassandra.CassandraProperties;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
 import org.springframework.boot.autoconfigure.domain.EntityScanPackages;
@@ -59,6 +60,7 @@ import org.springframework.data.cassandra.core.mapping.SimpleUserTypeResolver;
  */
 @Configuration
 @ConditionalOnClass({ Cluster.class, CassandraAdminOperations.class })
+@ConditionalOnBean(Cluster.class)
 @EnableConfigurationProperties(CassandraProperties.class)
 @AutoConfigureAfter(CassandraAutoConfiguration.class)
 public class CassandraDataAutoConfiguration {

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/data/cassandra/CassandraDataAutoConfigurationTests.java

@@ -105,6 +105,15 @@ public class CassandraDataAutoConfigurationTests {
 
 	}
 
+	@Test
+	void clusterDoesNotExist() {
+		AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
+		ctx.register(CassandraDataAutoConfiguration.class);
+		ctx.refresh();
+		this.context = ctx;
+		assertThat(ctx.getBeansOfType(Session.class)).isEmpty();
+	}
+
 	public void load(Class<?>... config) {
 		AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
 		TestPropertyValues.of("spring.data.cassandra.keyspaceName:boot_test")