Avoid calling Task.getProject() from a task action at execution time

Fix
```
> Task :spring-boot-project:spring-boot-tools:spring-boot-maven-plugin:formatHelpMojoSource
Invocation of Task.project at execution time has been deprecated. This will fail with an error in Gradle 9.0. Consult the upgrading guide for further information: https://docs.gradle.org/8.10.2/userguide/upgrading_version_7.html#task_project
```

Author: quaff

buildSrc/src/main/java/org/springframework/boot/build/mavenplugin/MavenPluginPlugin.java

@@ -106,6 +106,7 @@
  *
  * @author Andy Wilkinson
  * @author Phillip Webb
+ * @author Yanming Zhou
  */
 public class MavenPluginPlugin implements Plugin<Project> {
 
@@ -334,8 +335,14 @@ private void addExtractVersionPropertiesTask(Project project) {
 
 	public abstract static class FormatHelpMojoSource extends DefaultTask {
 
+		private final Project project;
+
 		private Task generator;
 
+		public FormatHelpMojoSource() {
+			this.project = getProject();
+		}
+
 		void setGenerator(Task generator) {
 			this.generator = generator;
 			getInputs().files(this.generator)
@@ -350,7 +357,7 @@ void setGenerator(Task generator) {
 		void syncAndFormat() {
 			FileFormatter formatter = new FileFormatter();
 			for (File output : this.generator.getOutputs().getFiles()) {
-				formatter.formatFiles(getProject().fileTree(output), StandardCharsets.UTF_8)
+				formatter.formatFiles(this.project.fileTree(output), StandardCharsets.UTF_8)
 					.forEach((edit) -> save(output, edit));
 			}
 		}