tiup playground can not deploy a right version cluster

[aytrack]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?

tiup playground vx.x.x

2. What did you expect to see?

deploy a cluster with expected version

3. What did you see instead?
   It always deploy a v8.0.0 cluster
   
   

4. What version of TiUP are you using (tiup --version)?
   

[JasonWu0506]

/label severity/critical

[ti-chi-bot]

@JasonWu0506: The label(s) severity/critical cannot be applied. These labels are supported: help wanted, good first issue.

In response to this:

/label severity/critical

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