Align usage of project_import_ndjson

Currently the `project_import_ndjson` is `default_enabled: true`.
Ensure that this holds true everywhere.

spec/support/import_export/common_util.rb

@@ -19,7 +19,7 @@ module ImportExport
     end
 
     def setup_reader(reader)
-      if reader == :ndjson_reader && Feature.enabled?(:project_import_ndjson)
+      if reader == :ndjson_reader && Feature.enabled?(:project_import_ndjson, default_enabled: true)
         allow_any_instance_of(Gitlab::ImportExport::JSON::LegacyReader::File).to receive(:exist?).and_return(false)
         allow_any_instance_of(Gitlab::ImportExport::JSON::NdjsonReader).to receive(:exist?).and_return(true)
       else