[Fix] Fix the bug that vit cannot load pretrain properly when using i… (#999)

* [Fix] Fix the bug that vit cannot load pretrain properly when using init_cfg to specify the pretrain scheme

* [Fix] fix the coverage problem

* Update mmseg/models/backbones/vit.py

Co-authored-by: Junjun2016 <hejunjun@sjtu.edu.cn>

* [Fix] make the predicate more concise and clearer

* [Fix] Modified the judgement logic

* Update tests/test_models/test_backbones/test_vit.py

Co-authored-by: Junjun2016 <hejunjun@sjtu.edu.cn>

* add comments

Co-authored-by: Junjun2016 <hejunjun@sjtu.edu.cn>