[Bug] VOCMetric is not compatible with CocoDataset

[RangiLyu]

Prerequisite

• I have searched Issues and Discussions but cannot get the expected help.
• I have read the FAQ documentation but cannot get the expected help.
• The bug has not been fixed in the latest version (master) or latest version (3.x).

Task

I have modified the scripts/configs, or I'm working on my own tasks/models/datasets.

Branch

3.x branch https://github.com/open-mmlab/mmdetection/tree/3.x

Environment

pass

Reproduces the problem - code sample

Reproduces the problem - command or script

pass

Reproduces the problem - error message

Additional information

Reported from Zihao.

This function should support custom class names

mmdetection/mmdet/evaluation/metrics/voc_metric.py

Line 136 in 61dd8d5

dataset_name = self.dataset_meta['classes']

mmdetection/mmdet/evaluation/metrics/voc_metric.py

Line 151 in 61dd8d5

dataset=dataset_name,

mmdetection/mmdet/evaluation/functional/class_names.py

Line 503 in 61dd8d5

def get_classes(dataset) -> list: