Tiup upgrade hit many warning like "invalid signature for file snapshot.json"

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?

2. What did you expect to see?
   Hit such warnings many time, not sure what is caused and how to fix.
   Warn: invalid signature for file snapshot.json: crypto/rsa: verification error
   Warn: invalid signature for file snapshot.json: crypto/rsa: verification error
   Warn: invalid signature for file snapshot.json: crypto/rsa: verification error
   Warn: invalid signature for file snapshot.json: crypto/rsa: verification error
   Warn: invalid signature for file snapshot.json: crypto/rsa: verification error
   Warn: invalid signature for file snapshot.json: crypto/rsa: verification error
   Warn: invalid signature for file snapshot.json: crypto/rsa: verification error
   Warn: invalid signature for file snapshot.json: crypto/rsa: verification error
   Warn: invalid signature for file snapshot.json: crypto/rsa: verification error
   Warn: invalid signature for file snapshot.json: crypto/rsa: verification error

3. What did you see instead?
   a、Should give more information about why and how to fix.
   b、No such warnings.

4. What version of TiUP are you using (tiup --version)?
   [root@436 brlog]# tiup --version
   1.10.3 tiup
   Go Version: go1.18.5
   Git Ref: v1.10.3
   GitHash: e198ac54996fa5a29f1961a460d6634ee9e75d2

Start by reproducing the TiUP upgrade command with the reported v1.10.3 environment and repeated snapshot.json signature warnings. Trace where the warning is emitted and determine why verification fails. Done means explaining the cause and either eliminating the spurious warnings or providing actionable remediation, with a regression check.