[Enhance] Add `ignore_keys` in ConcatDataset (#556)

* [Fix] Fix ConcatDataset error in VOCDataset

* minor fix

* minor fix

* minor fix

* add UT

* minor fix

* minor fix

* minor fix

* Update mmengine/dataset/dataset_wrapper.py

Co-authored-by: Zaida Zhou <58739961+zhouzaida@users.noreply.github.com>

* minor fix

* Update mmengine/dataset/dataset_wrapper.py

Co-authored-by: Zaida Zhou <58739961+zhouzaida@users.noreply.github.com>

Co-authored-by: Zaida Zhou <58739961+zhouzaida@users.noreply.github.com>