Merge pull request #27537 from izeye

* pr/27537:
  Use deprecated mainClassName in Gradle test

Closes gh-27537

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/resources/org/springframework/boot/gradle/tasks/bundling/BootJarIntegrationTests-basicBuildUsingDeprecatedMainClassName.gradle

@@ -4,5 +4,5 @@ plugins {
 }
 
 bootJar {
-	mainClass = 'com.example.Application'
+	mainClassName = 'com.example.Application'
 }