Fix cargoBuild being ran even for clean

[Mygod]

We probably should also register a cargoClean task like this:

tasks.register<Exec>("cargoClean") {
    executable("cargo")     // cargo.cargoCommand
    args("clean")
    workingDir("$projectDir/${cargo.module}")
}
tasks.clean.dependsOn("cargoClean")

[thomcc]

Thanks

[Mygod]

Do you think we should register this task (and also the cleaning task) within the plugin?

[Mygod]

Actually maybe it should be depended on by mergeDebugJniLibFolders and mergeReleaseJniLibFolders instead, but we should probably enable ExternalNativeBuild first.