[regression-test](pipeline) reduce tests concurrency (#38026)

## Proposed changes

Issue Number: close #xxx

<!--Describe your changes.-->

regression-test/pipeline/cloud_p0/run.sh

@@ -69,8 +69,8 @@ run() {
  --clean \
  --run \
  --times "${repeat_times_from_trigger:-1}" \
- -parallel 14 \
- -suiteParallel 14 \
+ -parallel 8 \
+ -suiteParallel 8 \
  -actionParallel 2; then
  echo
  else