Deprecation warning with Gradle 9

[gjvoosten]

Gradle 9 project.getProperties() has been deprecated:

> Task :graphql-gradle-plugin3:compileJava
…/graphql-gradle-plugin-project/graphql-gradle-plugin3/src/main/java/com/graphql_java_generator/gradleplugin/GraphQLPlugin.java:153: warning: [deprecation] getProperties() in Project has been deprecated
					SourceSet main = ((SourceSetContainer) project.getProperties().get("sourceSets"))
					                                              ^
…/graphql-gradle-plugin-project/graphql-gradle-plugin3/src/main/java/com/graphql_java_generator/gradleplugin/GraphQLPlugin.java:290: warning: [deprecation] getProperties() in Project has been deprecated
		SourceSet main = ((SourceSetContainer) project.getProperties().get("sourceSets"))
		                                              ^
2 warnings

Should be fixable with:

diff --git a/graphql-gradle-plugin3/src/main/java/com/graphql_java_generator/gradleplugin/GraphQLPlugin.java b/graphql-gradle-plugin3/src/main/java/com/graphql_java_generator/gradleplugin/GraphQLPlugin.java
index 7fbbc1f..72d30f1 100644
--- a/graphql-gradle-plugin3/src/main/java/com/graphql_java_generator/gradleplugin/GraphQLPlugin.java
+++ b/graphql-gradle-plugin3/src/main/java/com/graphql_java_generator/gradleplugin/GraphQLPlugin.java
@@ -150,8 +150,7 @@ public class GraphQLPlugin implements Plugin<Project> {
                                if (task instanceof GenerateCodeCommonTask) {
                                        GenerateCodeCommonTask t = (GenerateCodeCommonTask) task;
                                        // Let's add the folders where the sources and resources have been generated to the project
-                                       SourceSet main = ((SourceSetContainer) project.getProperties().get("sourceSets"))
-                                                       .getByName(SourceSet.MAIN_SOURCE_SET_NAME);
+                                       SourceSet main = getMainSourceSet(project);
                                        main.getJava().srcDir(t.getTargetSourceFolder());
 
                                        addGeneratedResourceFolder(project, task, t.getTargetResourceFolder());
@@ -182,6 +181,17 @@ public class GraphQLPlugin implements Plugin<Project> {
                return getProperties().get("graphqlMavenPluginLogic.version").toString();
        }
 
+       /**
+        * Get the main sourceSet of the project.
+        * 
+        * @param project the project
+        * @return the main sourceSet of the project
+        */
+       private SourceSet getMainSourceSet(Project project) {
+               return project.getExtensions().getByType(SourceSetContainer.class)
+                               .getByName(SourceSet.MAIN_SOURCE_SET_NAME);
+       }
+
        /** Manual reading of the application.properties file, as this is not a spring boot project. */
        private Properties getProperties() {
                if (properties == null) {
@@ -287,8 +297,7 @@ public class GraphQLPlugin implements Plugin<Project> {
 
        /** Add the given resource folder to the resource folders list, if it wasn't already added. */
        private void addGeneratedResourceFolder(Project project, Task task, File newResourcFolder) {
-               SourceSet main = ((SourceSetContainer) project.getProperties().get("sourceSets"))
-                               .getByName(SourceSet.MAIN_SOURCE_SET_NAME);
+               SourceSet main = getMainSourceSet(project);
                String newResourceFolder = newResourcFolder.getAbsolutePath();
                java.util.Optional<File> existingResourceFolder = main.getResources().getFiles().stream()
                                .filter(f -> f.getAbsolutePath().equals(newResourceFolder)).findFirst();