Address review comment: clarify disabled counter assertion in ExtendedMetricsApiUsageTest

Author: dashpole

api/incubator/src/test/java/io/opentelemetry/api/incubator/metrics/ExtendedMetricsApiUsageTest.java

@@ -182,6 +182,8 @@ void optInAdvice() {
     counter1.add(1);
     counter2.add(1);
 
+    // Verify that only counter1 is collected and measurements recorded to disabled counter2 are
+    // dropped
     assertThat(reader.collectAllMetrics())
         .satisfiesExactly(
             metricData ->