Fix gradle deprecations in Kotlin Native

Merge-request: KT-MR-10267
Merged-by: Cristian Garcia <Cristian.Garcia-Marin@jetbrains.com>

kotlin-native/backend.native/build.gradle

@@ -225,7 +225,7 @@ task external_jars(type: Copy) {
 
 task debugCompiler(type: JavaExec) {
     dependsOn ':dist'
-    main = 'org.jetbrains.kotlin.cli.bc.K2NativeKt'
+    mainClass = 'org.jetbrains.kotlin.cli.bc.K2NativeKt'
     classpath = project.fileTree("${distDir.canonicalPath}/konan/lib/") {
         include '*.jar'
     }