firestore: increase slack for update time checks
The tests were still failing on a GCP windows machine.
@@ -945,7 +945,7 @@ func copyMap(m map[string]interface{}) map[string]interface{} {
func checkTimeBetween(t *testing.T, got, low, high time.Time) {
// Allow slack for clock skew.
- const slack = 500 * time.Millisecond
+ const slack = 1 * time.Second
low = low.Add(-slack)
high = high.Add(slack)
if got.Before(low) || got.After(high) {
