[HDFS-16903]. Fix javadoc of LightWeightResizableGSet class (#5338)

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/LightWeightResizableGSet.java

@@ -33,7 +33,7 @@ import java.util.function.Consumer;
  *
  * This class does not support null element.
  *
- * This class is not thread safe.
+ * This class is thread safe.
  *
  * @param <K> Key type for looking up the elements
  * @param <E> Element type, which must be