test: fix TestHashKVWhenCompacting: ensure all goroutine finished

[ahrtr]

Fix #17232

• We should ensure all goroutines finished before exiting the test case
• Compaction 100 times may take longer than 10s, so reduce the count from 100 to 50;

Please read https://github.com/etcd-io/etcd/blob/main/CONTRIBUTING.md#contribution-flow.

[ahrtr]

Root cause:
When test timed out, it fails the test right away, and cleanup will be executed before exiting the test gouroutine, and the backend storage will be closed. The other two gouroutines may not have finished yet, so eventually run into nic porinter panicking.

• etcd/server/storage/mvcc/kvstore_test.go

  Line 569 in 15f95ec

  go func() {

• etcd/server/storage/mvcc/kvstore_test.go

  Line 587 in 15f95ec

  go func() {

[jmhbnz]

Ensuring all goroutines finished is a good catch.

Have a question below about halving compaction count.

Tested the change, didn't see any difference in results

[ahrtr]

/test pull-etcd-unit-test

[fuweid]

LGTM

[ahrtr]

ping @serathius