tests/integration: deflake #15409

The cluster version will be initialized after the member becomes leader.
The update is handled asynchronously. It couldn't be updated if the member
has been closed and the go-runtime picks the `s.stopping` channel first.

```go
// e2a5df534c/server/etcdserver/server.go (L2170)

func (s *EtcdServer) monitorClusterVersions() {
	...
	for {
		select {
		case <-s.firstCommitInTerm.Receive():
		case <-time.After(monitorVersionInterval):
		case <-s.stopping:
			return
		}
		...
	}
}
```

Or after the `s.stopping` has been closed, the [UpdateClusterVersion][1] won't
file GoAttach successfully. For the #15409, we can see the warn log
`server has stopped; skipping GoAttach` from GoAttach:

```plain
https://github.com/etcd-io/etcd/actions/runs/4340931587/jobs/7580103902

    logger.go:130: 2023-03-06T07:36:44.253Z	WARN	default	stopping grpc server due to error	{"error": "accept tcp 127.0.0.1:2379: use of closed network connection"}
    logger.go:130: 2023-03-06T07:36:44.253Z	WARN	default	stopped grpc server due to error	{"error": "accept tcp 127.0.0.1:2379: use of closed network connection"}
    logger.go:130: 2023-03-06T07:36:44.253Z	ERROR	default	setting up serving from embedded etcd failed.	{"error": "accept tcp 127.0.0.1:2379: use of closed network connection"}
    logger.go:130: 2023-03-06T07:36:44.253Z	ERROR	default	setting up serving from embedded etcd failed.	{"error": "http: Server closed"}
    logger.go:130: 2023-03-06T07:36:44.253Z	INFO	default	skipped leadership transfer for single voting member cluster	{"local-member-id": "8e9e05c52164694d", "current-leader-member-id": "8e9e05c52164694d"}

    logger.go:130: 2023-03-06T07:36:44.253Z	WARN	default	server has stopped; skipping GoAttach

    ...
```

If the cluster version isn't updated, the minimum storage version will
be v3.5 because the [AuthStatus][2] is introduced in [v3.5][3].
The compare will fail.

To fix this issue, we should wait for cluster version to become ready
after server is ready to serve request.

[1]: <e2a5df534c/server/etcdserver/adapters.go (L45)>
[2]: <071e70cdc4>
[3]: <1b4e54c238>

Signed-off-by: Wei Fu <fuweid89@gmail.com>

tests/integration/utl_wal_version_test.go

@@ -28,6 +28,7 @@ import (
 	"go.etcd.io/etcd/server/v3/embed"
 	"go.etcd.io/etcd/server/v3/storage/wal"
 	"go.etcd.io/etcd/server/v3/storage/wal/walpb"
+	framecfg "go.etcd.io/etcd/tests/v3/framework/config"
 	"go.etcd.io/etcd/tests/v3/framework/integration"
 )
 
@@ -45,28 +46,62 @@ func TestEtcdVersionFromWAL(t *testing.T) {
 		t.Fatalf("failed to start embed.Etcd for test")
 	}
 
+	// When the member becomes leader, it will update the cluster version
+	// with the cluster's minimum version. As it's updated asynchronously,
+	// it could not be updated in time before close. Wait for it to become
+	// ready.
+	if err := waitForClusterVersionReady(srv); err != nil {
+		srv.Close()
+		t.Fatalf("failed to wait for cluster version to become ready: %v", err)
+	}
+
 	ccfg := clientv3.Config{Endpoints: []string{cfg.ACUrls[0].String()}}
 	cli, err := integration.NewClient(t, ccfg)
 	if err != nil {
 		srv.Close()
 		t.Fatal(err)
 	}
-	// Get auth status to increase etcd version of proto stored in wal
+
+	// Once the cluster version has been updated, any entity's storage
+	// version should be align with cluster version.
 	ctx, cancel := context.WithTimeout(context.Background(), testutil.RequestTimeout)
-	cli.AuthStatus(ctx)
+	_, err = cli.AuthStatus(ctx)
 	cancel()
+	if err != nil {
+		srv.Close()
+		t.Fatalf("failed to get auth status: %v", err)
+	}
 
 	cli.Close()
 	srv.Close()
 
 	w, err := wal.Open(zap.NewNop(), cfg.Dir+"/member/wal", walpb.Snapshot{})
 	if err != nil {
-		panic(err)
+		t.Fatal(err)
 	}
 	defer w.Close()
+
 	walVersion, err := wal.ReadWALVersion(w)
 	if err != nil {
 		t.Fatal(err)
 	}
 	assert.Equal(t, &semver.Version{Major: 3, Minor: 6}, walVersion.MinimalEtcdVersion())
 }
+
+func waitForClusterVersionReady(srv *embed.Etcd) error {
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	defer cancel()
+
+	for {
+		select {
+		case <-ctx.Done():
+			return ctx.Err()
+		default:
+		}
+
+		if srv.Server.ClusterVersion() != nil {
+			return nil
+		}
+		time.Sleep(framecfg.TickDuration)
+	}
+}