[Cloud Spanner Change Streams] Fix inverted evaluation of cancelQueryOnHeartbeat (#38695)

This meant that low latency mode for heartbeats was enabled by default and disabled in low latency mode instead of the desired opposite.

Author: scwhittle

sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/spanner/changestreams/action/HeartbeatRecordAction.java

@@ -104,6 +104,6 @@ public Optional<ProcessContinuation> run(
       return Optional.empty();
     }
     // no new data, finish reading data
-    return cancelQueryOnHeartbeat ? Optional.empty() : Optional.of(ProcessContinuation.resume());
+    return cancelQueryOnHeartbeat ? Optional.of(ProcessContinuation.resume()) : Optional.empty();
   }
 }

sdks/java/io/google-cloud-platform/src/test/java/org/apache/beam/sdk/io/gcp/spanner/changestreams/action/HeartbeatRecordActionTest.java

@@ -232,7 +232,7 @@ public void testEndTimestampNotReachedOnCancellingAction() {
             watermarkEstimator,
             endTimestamp);
 
-    assertEquals(Optional.empty(), maybeContinuation);
+    assertEquals(Optional.of(ProcessContinuation.resume()), maybeContinuation);
     verify(watermarkEstimator).setWatermark(new Instant(timestamp.toSqlTimestamp().getTime()));
   }
 
@@ -254,7 +254,7 @@ public void testEndTimestampNotReachedOnAction() {
             watermarkEstimator,
             endTimestamp);
 
-    assertEquals(Optional.of(ProcessContinuation.resume()), maybeContinuation);
+    assertEquals(Optional.empty(), maybeContinuation);
     verify(watermarkEstimator).setWatermark(new Instant(timestamp.toSqlTimestamp().getTime()));
   }
 }