[Fix] Fix registry import error of mmdet

[fangyixiao18]

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Motivation

Related issue: https://github.com/open-mmlab/mmselfsup/issues/726

Modification

Please briefly describe what modification is made in this PR.

BC-breaking (Optional)

Does the modification introduce changes that break the backward compatibility of the downstream repositories? 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

Before PR:

• [ ] Pre-commit or other linting tools are used to fix the potential lint issues.
• [ ] Bug fixes are fully covered by unit tests, the case that causes the bug should be added in the unit tests.
• [ ] The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
• [ ] The documentation has been modified accordingly, like docstring or example tutorials.

After PR:

• [ ] If the modification has potential influence on downstream or other related projects, this PR should be tested with those projects, like MMDet or MMSeg.
• [ ] CLA has been signed and all committers have signed the CLA in this PR.

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.54 :tada:

Comparison is base (105ca79) 80.24% compared to head (ec0a79a) 80.79%.

:exclamation: Current head ec0a79a differs from pull request most recent head 88294d4. Consider uploading reports for the commit 88294d4 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev-1.x #732 +/- ## =========================================== + Coverage 80.24% 80.79% +0.54% =========================================== Files 141 144 +3 Lines 5129 5207 +78 Branches 687 693 +6 =========================================== + Hits 4116 4207 +91 + Misses 873 860 -13 Partials 140 140 ``` | Flag | Coverage Δ | | |---|---|---| | unittests | `80.79% <100.00%> (+0.54%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-mmlab#carryforward-flags-in-the-pull-request-comment) to find out more. | [Impacted Files](https://codecov.io/gh/open-mmlab/mmselfsup/pull/732?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-mmlab) | Coverage Δ | | |---|---|---| | [mmselfsup/registry.py](https://codecov.io/gh/open-mmlab/mmselfsup/pull/732?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-mmlab#diff-bW1zZWxmc3VwL3JlZ2lzdHJ5LnB5) | `100.00% <ø> (ø)` | | | [mmselfsup/datasets/transforms/\_\_init\_\_.py](https://codecov.io/gh/open-mmlab/mmselfsup/pull/732?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-mmlab#diff-bW1zZWxmc3VwL2RhdGFzZXRzL3RyYW5zZm9ybXMvX19pbml0X18ucHk=) | `100.00% <100.00%> (ø)` | | | [mmselfsup/datasets/transforms/pytorch\_transform.py](https://codecov.io/gh/open-mmlab/mmselfsup/pull/732?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-mmlab#diff-bW1zZWxmc3VwL2RhdGFzZXRzL3RyYW5zZm9ybXMvcHl0b3JjaF90cmFuc2Zvcm0ucHk=) | `100.00% <100.00%> (ø)` | | | [mmselfsup/models/algorithms/\_\_init\_\_.py](https://codecov.io/gh/open-mmlab/mmselfsup/pull/732?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-mmlab#diff-bW1zZWxmc3VwL21vZGVscy9hbGdvcml0aG1zL19faW5pdF9fLnB5) | `100.00% <100.00%> (ø)` | | | [mmselfsup/models/algorithms/pixmim.py](https://codecov.io/gh/open-mmlab/mmselfsup/pull/732?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-mmlab#diff-bW1zZWxmc3VwL21vZGVscy9hbGdvcml0aG1zL3BpeG1pbS5weQ==) | `100.00% <100.00%> (ø)` | | | [mmselfsup/models/target\_generators/\_\_init\_\_.py](https://codecov.io/gh/open-mmlab/mmselfsup/pull/732?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-mmlab#diff-bW1zZWxmc3VwL21vZGVscy90YXJnZXRfZ2VuZXJhdG9ycy9fX2luaXRfXy5weQ==) | `100.00% <100.00%> (ø)` | | | [...sup/models/target\_generators/low\_freq\_generator.py](https://codecov.io/gh/open-mmlab/mmselfsup/pull/732?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-mmlab#diff-bW1zZWxmc3VwL21vZGVscy90YXJnZXRfZ2VuZXJhdG9ycy9sb3dfZnJlcV9nZW5lcmF0b3IucHk=) | `100.00% <100.00%> (ø)` | | | [mmselfsup/models/utils/res\_layer\_extra\_norm.py](https://codecov.io/gh/open-mmlab/mmselfsup/pull/732?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-mmlab#diff-bW1zZWxmc3VwL21vZGVscy91dGlscy9yZXNfbGF5ZXJfZXh0cmFfbm9ybS5weQ==) | `47.36% <100.00%> (+15.78%)` | :arrow_up: | ... and [3 files with indirect coverage changes](https://codecov.io/gh/open-mmlab/mmselfsup/pull/732/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-mmlab) Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-mmlab). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-mmlab)

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