[Enhancement] Use round-robin

[MeowZheng]

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Motivation

1. daily-shift-based is not suited for assignees < 5

Modification

1. .owners.yml

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.

[codecov]

Codecov Report

Merging #1543 (e8d5bcc) into master (ae0fac4) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1543   +/-   ##
=======================================
  Coverage   90.40%   90.40%           
=======================================
  Files         141      141           
  Lines        8443     8443           
  Branches     1423     1423           
=======================================
  Hits         7633     7633           
  Misses        572      572           
  Partials      238      238           

Flag	Coverage Δ
unittests	90.40% <ø> (ø)

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