Add macOS CI

[zhouzaida]

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Motivation

Add macOS CI.

Modification

Please briefly describe what modification is made in this PR.

BC-breaking (Optional)

Does the modification introduce changes that break the back-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 MMCls.
4. The documentation has been modified accordingly, like docstring or example tutorials.

[codecov]

Codecov Report

Merging #138 (4d8f517) into main (3276085) will not change coverage.
The diff coverage is n/a.

❗ Current head 4d8f517 differs from pull request most recent head 54a066a. Consider uploading reports for the commit 54a066a to get more accurate results

@@           Coverage Diff           @@
##             main     #138   +/-   ##
=======================================
  Coverage   53.59%   53.59%           
=======================================
  Files          22       22           
  Lines        1532     1532           
  Branches      328      328           
=======================================
  Hits          821      821           
  Misses        585      585           
  Partials      126      126           

Flag	Coverage Δ
unittests	53.59% <ø> (ø)

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