Fix 'kotlinOptions.jdkHome' deprecation message typo.

Use proper DSL example how-to set toolchain.

^KT-48768 Fixed

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/internal/CompilerArgumentsContributor.kt

@@ -121,7 +121,7 @@ internal open class KotlinJvmCompilerArgumentsContributor(
                     
                     Consider using JavaToolchain on Gradle 6.7+:
                     kotlin {
-                        toolchain {
+                        jvmToolchain {
                             languageVersion.set(JavaLanguageVersion.of(<MAJOR_JDK_VERSION>))
                         }
                     }