Test our Gradle plugin against Gradle 7.1

Closes gh-26904

Author: wilkinsona

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", "7.1-rc-2");
+			GRADLE_VERSIONS = Arrays.asList("7.0.2", "7.1");
 		}
 		else {
-			GRADLE_VERSIONS = Arrays.asList("6.8.3", "current", "7.0.2", "7.1-rc-2");
+			GRADLE_VERSIONS = Arrays.asList("6.8.3", "current", "7.0.2", "7.1");
 		}
 	}