xdsclient: Fix flakyness in TestResourceUpdateMetrics in the case of repeated NACKs (#8363)

Author: purnesh42H

xds/internal/clients/xdsclient/test/helpers_test.go

@@ -296,5 +296,5 @@ func (r *testMetricsReporter) waitForMetric(ctx context.Context, metricsDataWant
 
 // ReportMetric sends the metrics data to the metricsCh channel.
 func (r *testMetricsReporter) ReportMetric(m any) {
-	r.metricsCh.Send(m)
+	r.metricsCh.Replace(m)
 }

xds/internal/clients/xdsclient/test/metrics_test.go

@@ -40,7 +40,7 @@ import (
 // to send valid and invalid LDS updates, and verifies that the expected metrics
 // for both good and bad updates are emitted.
 func (s) TestResourceUpdateMetrics(t *testing.T) {
-	ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout*1000)
+	ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
 	defer cancel()
 
 	tmr := newTestMetricsReporter()