Work around too eager modification of `compileJava.destinationDir` by Java Modularity Plugin

[tlinkowski]

This plugin configures Kotlin for subprojects only for test. But the modularity plugin changes the destination directory for compileJava or compileModuleInfoJava even if there are no Kotlin sources in main.

https://github.com/java9-modularity/gradle-modules-plugin/blob/44a76f62965d93a45422f62f16fb75ef6e3fe13d/src/main/java/org/javamodularity/moduleplugin/tasks/CompileJavaTaskMutator.java#L44-L46