Changes

ci: replace deprecated PingCAP chart domains (#4452)

## Summary
- replace deprecated `charts.pingcap.org` references in the TiDB
Operator release pipeline
- keep the existing old download-domain compatibility rewrite logic
intact

## Validation
- `git diff --check`
- verified no remaining `charts.pingcap.org` matches in the touched file
 (commit: c2f4d0d)