fix(generator): replace array_merge_recursive with array_replace_recursive

Issue #3019569 by akalam: Overrides over destination.plugin are added instead of replaced, resulting in an array of destination plugins

Closes #3019569

src/MigrationGenerator.php

@@ -402,7 +402,7 @@ class MigrationGenerator implements MigrationGeneratorInterface {
     if (file_exists($override_file_path)) {
       $yaml = new Parser();
       $override = $yaml->parse(file_get_contents($override_file_path));
-      $migration_plugin = array_merge_recursive($migration_plugin, $override);
+      $migration_plugin = array_replace_recursive($migration_plugin, $override);
     }
     return $migration_plugin;
   }