BUG FIX in test_cfg for U-Net _base_ scripts

[smttsp]

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

Please describe the motivation of this PR and the goal you want to achieve through this PR.

Bug fix on base U-Net scripts: The base U-Net scripts contain some variables in wrong type in test_cfg dictionary. The stride and crop_size fields in this dict are supposed to be tuples(int, int), however, they are int which result in the following exception at validation step:

h_stride, w_stride = self.test_cfg.stride TypeError: cannot unpack non-iterable int object

An issue is created (#2337) and this PR aims to fix it

Modification

Please briefly describe what modification is made in this PR.

changing stride and crop_size from int to (int, int)

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: No impact on formatting
2. The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness: couldn't find any unit-tests for configs
3. If the modification has potential influence on downstream projects, this PR should be tested with downstream projects, like MMDet or MMDet3D: No impact
4. The documentation has been modified accordingly, like docstring or example tutorials: I need help with this

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

Base: 88.96% // Head: 88.97% // Increases project coverage by +0.01% 🎉

Coverage data is based on head (bd87c92) compared to base (1bb58de).
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2347      +/-   ##
==========================================
+ Coverage   88.96%   88.97%   +0.01%     
==========================================
  Files         146      146              
  Lines        8746     8746              
  Branches     1474     1474              
==========================================
+ Hits         7781     7782       +1     
  Misses        722      722              
+ Partials      243      242       -1     

Flag	Coverage Δ
unittests	88.97% <ø> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
mmseg/datasets/pipelines/transforms.py	98.83% <0.00%> (+0.19%)	⬆️

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[jason102811]

smttsp，您好！您在MMSeg项目中给我们提的PR非常重要，感谢您付出私人时间帮助改进开源项目，相信很多开发者会从你的PR中受益。
我们非常期待与您继续合作，OpenMMLab专门成立了贡献者组织MMSIG，为贡献者们提供开源证书、荣誉体系和专享好礼，可通过添加微信：openmmlabwx 联系我们（请备注mmsig+GitHub id），由衷希望您能加入！
Dear smttsp,
First of all, we want to express our gratitude for your significant PR in the MMSeg project. Your contribution is highly appreciated, and we are grateful for your efforts in helping improve this open-source project during your personal time. We believe that many developers will benefit from your PR.
We are looking forward to continuing our collaboration with you. OpenMMLab has established a special contributors' organization called MMSIG, which provides contributors with open-source certificates, a recognition system, and exclusive rewards. You can contact us by adding our WeChat（if you have WeChat): openmmlab_wx, or join in our discord： https://discord.gg/qH9fysxPDW. We sincerely hope you will join us!
Best regards！ @smttsp