chore: make ide-plugin compatible with Gradle 9

Author: vlsi

plugins/ide-plugin/src/main/kotlin/com/github/vlsi/gradle/ide/IdeExtension.kt

@@ -28,6 +28,7 @@ import org.gradle.kotlin.dsl.apply
 import org.gradle.kotlin.dsl.configure
 import org.gradle.plugins.ide.eclipse.model.EclipseModel
 import org.gradle.plugins.ide.idea.model.IdeaModel
+import org.gradle.plugins.ide.idea.model.IdeaModule
 import org.gradle.util.GradleVersion
 import org.jetbrains.gradle.ext.ProjectSettings
 import java.io.File
@@ -111,8 +112,11 @@ open class IdeExtension(private val project: Project) {
                 if (GradleVersion.current() >= GradleVersion.version("7.4")) {
                     module.testSources.from(generationOutput)
                 } else {
-                    @Suppress("DEPRECATION")
-                    module.testSourceDirs.add(generationOutput)
+                    val getTestSourceDirs =
+                        IdeaModule::class.java.getDeclaredMethod("getTestSourceDirs")
+                    @Suppress("UNCHECKED_CAST")
+                    val testSourceDirs = getTestSourceDirs.invoke(module) as MutableSet<File>
+                    testSourceDirs.add(generationOutput)
                 }
             }
         }