[Fix] Add contiguous after permutation in ViT

[HarborYuan]

Thanks for your contribution and we appreciate it a lot. The following instructions would make your pull request more healthy and more easily get feedback. If you do not understand some items, don't worry, just make the pull request and seek help from maintainers.

Motivation

Similar with swin impl

Modification

Trivial modification

BC-breaking (Optional)

Does the modification introduce changes that break the backward-compatibility of the downstream repos?
If so, please describe how it breaks the compatibility and how the downstream projects should modify their code to keep compatibility with this PR.

Use cases (Optional)

If this PR introduces a new feature, it is better to list some use cases here, and update the documentation.

Checklist

1. Pre-commit or other linting tools are used to fix the potential lint issues.
2. The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
3. If the modification has potential influence on downstream projects, this PR should be tested with downstream projects, like MMDet or MMDet3D.
4. The documentation has been modified accordingly, like docstring or example tutorials.

[Junjun2016]

Hi @HarborYuan
Thanks for your contribution.

[Junjun2016]

Hi @HarborYuan
The CI has been fixed, please merge the master branch.

[HarborYuan]

Hi @HarborYuan
The CI has been fixed, please merge the master branch.

Merge the master branch? @Junjun2016

[Junjun2016]

Hi @HarborYuan
The CI has been fixed, please merge the master branch.

Merge the master branch? @Junjun2016

Yes, we have updated the CI in PR #994 (merged), so please merge the upstream master to your PR.

[codecov]

Codecov Report

Merging #992 (3450626) into master (e27017e) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #992   +/-   ##
=======================================
  Coverage   89.85%   89.85%           
=======================================
  Files         118      118           
  Lines        6558     6558           
  Branches     1019     1019           
=======================================
  Hits         5893     5893           
  Misses        464      464           
  Partials      201      201           

Flag	Coverage Δ
unittests	89.85% <ø> (ø)

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Impacted Files	Coverage Δ
mmseg/models/backbones/vit.py	87.11% <ø> (ø)

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