testing(bigquery/storeage/managedwriter): adjust testing boundaries (#…

…10028)

This PR gives a few of the longer-running managedwriter tests a haircut
by reducing iterations.  In many of these cases we're testing for
unusual race conditions and concurrency behaviors, so slightly longer
wall times are to be expected.

Measurement:

On my local cloudtop, `go test -race -short` for the managedwriter package
drops from ~92s to ~42s.

bigquery/storage/managedwriter/managed_stream_test.go

@@ -471,7 +471,7 @@ func TestManagedStream_LeakingGoroutines(t *testing.T) {
 
 	// Send a bunch of appends that expire quicker than response, and monitor that
 	// goroutine growth stays within bounded threshold.
-	for i := 0; i < 500; i++ {
+	for i := 0; i < 250; i++ {
 		expireCtx, cancel := context.WithTimeout(ctx, 25*time.Millisecond)
 		defer cancel()
 		ms.AppendRows(expireCtx, fakeData)
@@ -523,7 +523,7 @@ func TestManagedStream_LeakingGoroutinesReconnect(t *testing.T) {
 
 	// Send a bunch of appends that will trigger reconnects and monitor that
 	// goroutine growth stays within bounded threshold.
-	for i := 0; i < 100; i++ {
+	for i := 0; i < 30; i++ {
 		writeCtx := context.Background()
 		r, err := ms.AppendRows(writeCtx, fakeData)
 		if err != nil {
@@ -703,7 +703,7 @@ func TestManagedStream_RaceFinder(t *testing.T) {
 	}
 
 	numWriters := 5
-	numWrites := 50
+	numWrites := 15
 
 	var wg sync.WaitGroup
 	wg.Add(numWriters)