Needs approval from an approver in each of these files:
- ~~[OWNERS](https://github.com/zilliztech/milvus-helm/blob/master/OWNERS)~~ [LoveEachDay,haorenfsa]
Approvers can indicate their approval by writing `/approve` in a comment
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What this PR does / why we need it:
update readme for 4.2.21+ Compatibility Notice
Checklist
[Place an '[x]' (no spaces) in all applicable fields. Please remove unrelated fields.]
[mychartname]
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