Changes

ci(prow): update tiflow wip presubmits to use default cluster (#4328)

- Change cluster from gcp-prow-ksyun to default
- Update base image to
ghcr.io/pingcap-qe/ci/base:v2026.3.8-1-g9d412f4-go1.25
- Remove GO_PROXY, GOMODCACHE, GOCACHE environment variables
- Remove persistent volume claims for go cache
- Adjust resource requests and limits


Close #4237
 (commit: fd82bcd)