update comment about kotlin("jvm") apply false in test project (#4355)

Author: adam-enko

dokka-runners/dokka-gradle-plugin/src/testFixtures/kotlin/projects/MultiModuleProject.kt

@@ -34,8 +34,8 @@ fun TestScope.initMultiModuleProject(
 
         buildGradleKts = """
             |plugins {
-            |  // Kotlin plugin shouldn't be necessary here, but without it Dokka errors
-            |  // with ClassNotFound KotlinPluginExtension... very weird
+            |  // Must apply KGP in the root project ensure consistent classpath, 
+            |  // preventing issues like https://github.com/gradle/gradle/issues/17559 and https://github.com/gradle/gradle/issues/27218
             |  kotlin("jvm") version embeddedKotlinVersion apply false
             |  id("org.jetbrains.dokka") version "${DokkaConstants.DOKKA_VERSION}"
             |  id("org.jetbrains.dokka-javadoc") version "${DokkaConstants.DOKKA_VERSION}"