springboot Fix warnings in spring-boot-autoconfigure's Kotlin test code

w: spring-boot-project/spring-boot-autoconfigure/src/test/kotlin/org/springframework/boot/autoconfigure/diagnostics/analyzer/KotlinNoSuchBeanFailureAnalyzerNoKotlinReflectTests.kt: (32, 111): Unnecessary non-null assertion (!!) on a non-null receiver of type Class<String>
w: spring-boot-project/spring-boot-autoconfigure/src/test/kotlin/org/springframework/boot/autoconfigure/diagnostics/analyzer/KotlinNoSuchBeanFailureAnalyzerNoKotlinReflectTests.kt: (33, 22): Unnecessary non-null assertion (!!) on a non-null receiver of type FailureAnalysis
w: spring-boot-project/spring-boot-autoconfigure/src/test/kotlin/org/springframework/boot/autoconfigure/diagnostics/analyzer/KotlinNoSuchBeanFailureAnalyzerNoKotlinReflectTests.kt: (34, 220): Unnecessary non-null assertion (!!) on a non-null receiver of type Class<KotlinNoSuchBeanFailureAnalyzerNoKotlinReflectTests.ConstructorBoundProperties>