refactor(yarn)!: Make loadWorkspaceSubmodules() private

As of the recent refactoring of `Pnpm`, the is no more override of this
function in ORT. So, make the function private.

Signed-off-by: Frank Viernau <frank_viernau@epam.com>

plugins/package-managers/node/src/main/kotlin/Yarn.kt

@@ -118,7 +118,7 @@ open class Yarn(
     /**
      * Load the submodule directories of the project defined in [moduleDir].
      */
-    protected open fun loadWorkspaceSubmodules(moduleDir: File): Set<File> {
+    private fun loadWorkspaceSubmodules(moduleDir: File): Set<File> {
         val nodeModulesDir = moduleDir.resolve("node_modules")
         if (!nodeModulesDir.isDirectory) return emptySet()