ci(pipelines): unify checkout credentials usage in tidb/ticdc (#4288)
## Summary - unify checkout credentials handling across `pipelines/pingcap/tidb` and `pipelines/pingcap/ticdc` - make `checkoutRefs`/`checkoutRefsWithCacheLock` callsites use `GIT_CREDENTIALS_ID` consistently - set `GIT_CREDENTIALS_ID` to `'github-sre-bot-ssh'` for release-8.5 tasks that were empty
## Notes - keep `checkoutRefsWithCacheLock` argument order aligned with method signature (`timeout` before `credentialsId`) - scope limited to pipeline files