Include 6.9.x in version requirements message

Fixes gh-26952

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/plugin/SpringBootPlugin.java

@@ -99,8 +99,8 @@ public class SpringBootPlugin implements Plugin<Project> {
 	private void verifyGradleVersion() {
 		GradleVersion currentVersion = GradleVersion.current();
 		if (currentVersion.compareTo(GradleVersion.version("6.8")) < 0) {
-			throw new GradleException(
-					"Spring Boot plugin requires Gradle 6.8.x or 7.x. " + "The current version is " + currentVersion);
+			throw new GradleException("Spring Boot plugin requires Gradle 6.8.x, 6.9.x, or 7.x. "
+					+ "The current version is " + currentVersion);
 		}
 	}
 

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

@@ -41,8 +41,8 @@ class SpringBootPluginIntegrationTests {
 	@Test
 	void failFastWithVersionOfGradle6LowerThanRequired() {
 		BuildResult result = this.gradleBuild.gradleVersion("6.7.1").buildAndFail();
-		assertThat(result.getOutput())
-				.contains("Spring Boot plugin requires Gradle 6.8.x or 7.x. The current version is Gradle 6.7.1");
+		assertThat(result.getOutput()).contains(
+				"Spring Boot plugin requires Gradle 6.8.x, 6.9.x, or 7.x. The current version is Gradle 6.7.1");
 	}
 
 	@DisabledForJreRange(min = JRE.JAVA_16)