Test our Gradle plugin against 7.1-rc-1

7.1-rc-1 deprecates JavaExec's main property in favor of mainClass
which was introduced in Gradle 6.4. This commit updates some tests
to use mainClass rather than main that would otherwise have failed
due to deprecation warnings in their output.

Closes gh-26793

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/java/org/springframework/boot/gradle/junit/GradleCompatibilityExtension.java

@@ -48,10 +48,10 @@ final class GradleCompatibilityExtension implements TestTemplateInvocationContex
 	static {
 		JavaVersion javaVersion = JavaVersion.current();
 		if (javaVersion.isCompatibleWith(JavaVersion.VERSION_16)) {
-			GRADLE_VERSIONS = Arrays.asList("7.0.2");
+			GRADLE_VERSIONS = Arrays.asList("7.0.2", "7.1-rc-1");
 		}
 		else {
-			GRADLE_VERSIONS = Arrays.asList("6.8.3", "current", "7.0.2");
+			GRADLE_VERSIONS = Arrays.asList("6.8.3", "current", "7.0.2", "7.1-rc-1");
 		}
 	}
 

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

@@ -21,5 +21,5 @@ task explode(type: Sync) {
 
 task launch(type: JavaExec) {
 	classpath = files(explode)
-	main = 'org.springframework.boot.loader.JarLauncher'
+	mainClass = 'org.springframework.boot.loader.JarLauncher'
 }

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/resources/org/springframework/boot/gradle/tasks/run/BootRunIntegrationTests-applicationPluginMainClassNameIsNotUsedWhenItIsNull.gradle

@@ -5,6 +5,6 @@ plugins {
 
 bootRun {
 	doFirst {
-		println "Main class name = ${bootRun.main}"
+		println "Main class name = ${bootRun.mainClass.get()}"
 	}
 }